You need to look at the domain registrar's TOS to determine their polices for canceling a domain after the fact in the way they did, i.e. claiming the domain is "premium" and as such allowing them to cancel and raise the price and re-offer the domain.
The registrar may, in fact, have such a policy in their TOS that you agreed to when you opened an account with them and registered a domain. "Clicking through" and accepting a TOS is a binding contract. Their policy may hinge on an "escrow" hold on the domain for a certain time until your payment clears, they do due diligence, or other reasons, and by agreeing to the TOS you allowed them to reserve the right to cancel or re-offer the registration.
However, such a policy is at least (I think) ethically challenged and at most could be illegal - US and local laws in your your jurisdiction may come into play - in terms of ICANN's policies. You may have success opening a complaint with ICANN, the international organization that oversees domain registrars and works to resolve complaints such as cyber-squatting, issues with the way registrars operate, etc. See Registrant Rights and Responsibilities Under the 2009 Registrar Accreditation Agreement - ICANN.
If the registrar doesn't have a clear policy on the form of cancellation and re-offer you have been subjected to, your next step is definitely looking at Dispute Resolution Options - ICANN.
Keep all your documents and emails, and log all phone calls or chats with the registrar. Make screenshots of your Cloudflare account and Google's web cache.
And, it might be helpful to do a Google search for that registrar and "domain cancellation" or more relevant keywords to see if anything similar has happened in the past and the outcomes; those stories may give you ideas for other options. You may also need to find a local lawyer to advise you on your next steps, or talk to a free legal aid clinic in your area.
