Send a 93a demand letter.
On the 49 out of 50 chance that OP is not in Massachusetts, Chapter 93A of Massachusetts General Laws is the state's Consumer Protection Act.
A 93a demand letter is an official letter sent prior to filing a lawsuit against someone else. The letter describes the wrongful acts of the other party along with the “demands” requiring a response within
thirty (30) days. The letter may be used for deceptive practices by a business such as bait-and-switch tactics, selling defective items, failure to refund, or any other issues covered by the Massachusetts Consumer Protection Act.
https://www.mass.gov/service-details/30-day-demand-letter
Provides a sample demand letter that can probably be modified and used in any state by referring to the individual state's own version of a consumer protection law.
However, one should not threaten litigation unless one is prepared to engage in litigation.