Ex-client Trying To Bully Me?

I own a service business where clients have monthly memberships. One ex-client has been a headache for almost five years and is negative, condescending to my staff, and is always asking for special accommodations. Ex-client would also catch my staff after their shifts and talk with them for an hour+ about all of the things ex-client hates about the business. Staff has been great and always repeats back to me what client has said. Most of the complaints are just preferences and things that we cannot or are not willing to change.

We have always been kind and understanding for the most part but ex-client makes everyone feel uneasy. Ex-client’s latest issue has been the lighting and claims that when we do services, the lights need to be dimmed. We have always accommodated ex-client when asked but a few weeks ago, ex-client sent me an official letter from a doctor saying that for medical reasons we must dim the lights and that ex-client shouldn’t have to request it first. Ex-client wanted “official documentation of request” for “legal purposes”.

We have lots of clients during business hours and it is not always practical to have lights dimmed and sometimes we just forget. But every time ex-client has asked, we have always dimmed the lights.

The letter from the doctor was my final straw and I got a lawyer involved to make sure everything we did was legal. Lawyer said we can terminate ex-client’s membership so we did.

Ex-client is now claiming ADA laws (ex-client has a disability, I guess? That was news to me) and stating that we discriminated against ex-client by terminating their membership and not always dimming the lights.

We received a letter from a law firm today saying we must reinstate ex-client’s membership. My lawyer can’t look into this until after the new year and there is no way in hell I will ever allow ex-client back to terrorize me and my staff again. The energy has been significantly better since ex-client is gone.

Are my hands tied? We are a small business but are 100% ADA complaint. Will we have to reinstate ex-client’s membership because of ADA laws?