You can either affirmatively sue the optometrist for a "declaratory judgment" (court determination) that you do not owe the money (and that they cannot put this into collections or report to the credit rating agencies); or if you don't want to go to the cost or effort of initiating a lawsuit, you can wait to see if the optometrist or their collections agency sues you (since if they don't sue you and win, they can't make you pay), then defend against the lawsui, at the end of which, if the court agrees you do not owe the money, their debt will be dismissed. Unfortunately, those are you only effective options; you need a court to settle the issue, one way or another. If you want to initiate a lawsuit, you can hire an attorney or, if you want to represent yourself ("pro se"), contact the county court clerk's office for instructions.