Under the FDPC sec 809 (15 USC 1692h) a debt collection must send to the person from whom it is trying to collect the following information, within 5 days of the initial contact, if the info is not in the initial contact document:
(1) the amount of the debt;
(2) the name of the creditor to whom the debt is owed;
(3) a statement that unless the consumer, within thirty days after receipt of the notice, disputes the validity of the debt, or any portion thereof, the debt will be assumed to be valid by the debt collector;
(4) a statement that if the consumer notifies the debt collector in writing within the thirty-day period that the debt, or any portion thereof, is disputed, the debt collector will obtain verification of the debt or a copy of a judgment against the consumer and a copy of such verification or judgment will be mailed to the consumer by the debt collector; and
(5) a statement that, upon the consumer's written request within the thirty-day period, the debt collector will provide the consumer with the name and address of the original creditor, if different from the current creditor.
Item (4) in this list is supposed to notify the alleged debtor of his or her right to dispute the debt. The collector is not required to obtain verification of the debt beyond its initial assignment and the info in (1)-(3) above, unless the debtor requests it or disputes the debt (or part of it).
If the debt is disputed the collector must "verify" it. This can be a court judgment, but can also be a simple statement from the creditor that the debt is valid. Whatever verification it obtains must be provided to the alleged debtor.
There is also a Maryland Consumer Debt Collection Act (MCDCA), but it deals mostly with prohibiting threats by the collector, and does not impose any additional requirement to verify or validate the debt beyond what the FDPC requires.
If the debt collector complied with the FDPC, it is not liable for having attempted to collect an invalid debt. Note that under sec 807 of the FDPC a collector may not make false statements, including an attempt to collect a debt which the collector knows is not owed, and under sec 808 various "unfair practices" are prohibited. (This includes threatening a report to a credit agency if no such report is intended.) But if the collector does not know that the debt is invalid, it is not required to try to find out, and it is not an unfair practice to try to collect a debt that eventually proves to be invalid.
So the answer to your Q1 is yes, the collector has no such responsibility. Such laws are often a compromise between the regulated industry (in this case, collection agencies) who want minimal regulation, and consumer advocates.
As to your Q2, if the physician or the billing agents for the physician were negligent, or knowingly in violation of their contract, you may have a claim of action against them. But the amount you could collect would probably be limited to any actual damages you sustained, and if you did not have to actually pay the invalid debt, you would need to establish what actual costs were imposed on you. This would probably not be a huge sum.
There are lawyers who will take a case 'on contingency" where they are paid only if the claim is successful. But most will only do this if the potential judgment is large enough to pay their overhead if the case is won, and the chance of winning seems reasonable. Each law firm will have its own standards and policies in such matters.
Many lawyers offer free or low cost initial consultations, in which you could present the facts and the lawyer could say whether s/he would take the case, and on what basis, and give you an estimate of possible recovery and probable expenses. It might be a good idea to explore such an inquiry. The risks of that would be low.