They recently took me to court (I am now 20) to have me start paying
for the bill, under distress I signed paperwork stating that I'd start
paying them, however I find this entire situation very aggravating.
You are almost surely screwed at this point and can't do anything but abide by the settlement that you agreed to when you signed the paperwork.
Preface Regarding The Applicable Jurisdiction
I am answering based upon the majority rules of law in U.S. states, because there is almost no other country in the world where you could end up in this financial situation due to universal healthcare systems that exist in most countries other than the United States.
Also, this isn't an area of law with a great deal of state to state variation, although the law isn't exactly the same in every single U.S. state.
The Minority Defense
You quite possibly had a minority defense before you signed the paperwork. The minority defense is based upon an inability to give adequate consent to a contract.
Whether the minority defense would have worked in this case, however, is a close call, because there are exceptions to the rule that would probably apply in this case.
Settlement, Ratification and Duress
The legal standard for "duress" in contract law usually means situations where there is literally a gun to your head or they're going to kill your dog or something like that, not the kind of economic pressure or persistent harassing collection efforts that I suspect you are referring to in this case.
Of course, if they did steal your dog and threaten to kill it if you didn't sign the paperwork, then you really would have signed it under duress and you should probably both take legal action to repudiate that paperwork (because agreements entered into under duress are generally voidable, rather than void), and you should probably report the incident to the police as a crime.
So, anyway, the paperwork you signed is probably enforceable, despite the pressure that they put on you to sign it.
Once you sign a settlement agreement as an adult (which is almost surely what you did) you have ratified the agreement made when you were a minor and forfeit any way to fight it. You are stuck with what you agreed to at this point and there is nothing you can do about it short of going bankrupt.
I would not recommend going bankrupt over a debts owed to a single medical provider unless that debt is so huge that ruining your credit for seven years and paying a bankruptcy lawyer is worth it to get out of this debt. For most twenty-year-olds facing debts for a few chiropractor treatments this would not make sense.
Lesson learned: Talk to a lawyer before you sign paperwork, not afterwards, because once you've signed on the dotted line, there is usually little or nothing that a lawyer can do to help you at that point.
As a guarantor of the obligation to pay for your care, your mother would no doubt be on the hook in any case, whether or not you settled, and whether or not you went bankrupt. Unless the settlement agreement that you signed says otherwise, they can still attempt to collect the bill from her as well as from you.
Of course, as you make payments towards the total balance due, the total balance due goes down. Your mother, as a guarantor, is only obligated to pay the portion of the bills that remain unpaid when they try to collect the debt from her.
The Necessaries Exception To The Minority Defense
Even though the minority defense might apply in this situation, most states recognize an exception to the minority defense when a purchase of "necessaries" is made by a minor. Bills for medical care would usually count as "necessaries", because you would have had no choice but to buy if you had been an adult anyway, so your lack of consent to pay isn't something that caused you material harm.
Honestly, in the medical industry, an agreement in advance to pay a negotiated price is the exception rather than the norm.
Often the providers themselves have no real clear idea what their patients are billed for their services, although chiropractors tend to be more informed about the financial arrangements than medical doctors in most cases.
Void Contracts v. Voidable Contracts
In any case, minority is a defense to a contractual obligation that would ordinarily only make the contract voidable, rather than void.
In other words, a minor can repudiate a contract that is voidable on account of minority and successfully get out of it within a reasonable time of becoming an adult (or sooner while you are still a minor through a parent or guardian or next friend), but it is not automatically invalid. There is a good chance that a court would consider a two year delay in trying to repudiate the contractual obligation too long, even if it concluded that the necessaries doctrine did not apply because, for example, the court considered this to be elective, luxury care rather than medically necessary services.
Unjust Enrichment Claims
Also, in addition to suing for breach of contract, the chiropractor might be able to sue for quantum meruit. This legal theory is not based upon mutual consent the way a contract claim is, although this is sometimes called a "quasi-contract" or "implied contract" claim (it is also sometimes called a "restitution" or "unjust enrichment" claim). As a result, minority is not usually a defense to a quantum meruit claim.
Instead, a quantum meruit claim is based upon preventing you from being unjustly enriched, (1) from benefits that you received, (2) that were not unwelcome, (3) from the efforts of someone else who did that work, (4) with a reasonable expectation of being compensated for the work, (5) in situations where there is no binding contract between the parties. (Different lawyers and different courts might break up these elements into more or fewer components, but the gist of the claim would be the same in pretty much any state.)
In a quantum meruit case, damages are based upon the fair market value of the services rendered, rather than an agreement of the parties, since there was no mutually agreed price under a contract that they are seeking to enforce.
Quantum meruit claims are frequently brought as a backup claim to a claim for breach of contract by failing to pay for services, in cases where the contract claim may be infirm for reasons such as minority.