It is possible that the lawyer was not getting paid and stopped working on the matter. It is possible that the lawyer misplaced your communication or simply is busy with other matters. It is also possible that the lawyer's client does not have the money to pursue you. However, it is also very possible that the lawyer is preparing a lawsuit or a UDRP proceeding against you. You might want to follow-up with the lawyer and determine the status. Otherwise, you can wait and hope it goes away. However, if there is a good argument for infringement, continued use of the mark may only help the claim of willful infringement.
This is not legal advice. Even if it were, fee legal advice is worth what you pay for it. The facts of every case are different and should be addressed by a competent attorney who has all of the facts.