I am a lawyer and normally my advice would be to consult a lawyer. And, if you can find a lawyer to do an initial consultation for free, I'd do that. However,

I am a lawyer and normally my advice would be to consult a lawyer. And, if you can find a lawyer to do an initial consultation for free, I'd do that. However, in the case where you think the other party is bluffing, I would not hire a lawyer right away. The other party's only enforcement option is suing you. If they sue you, then hire a lawyer. The big issue is whether to respond. If you don't respond, they will stop contacting you after a certain number of attempts. If you do respond, you will get their attention. That can be good if you think you have a strong defense like mistaken identity or something. If I were you, I would ignore them and see if they sue. Edit: I looked up Lemer & Company and they are personal injury lawyers, not patent attorneys. They were probably hired only to write scary letters, which is more reason to ignore them until if or when they refer the case to patent counsel for litigation.