Prescription scare

Hi, I am on a contribution based esa, recently applied for an income based ESA.

I am staying in an independent flat where I was moved into by a charity.

For many years now I had been claiming free prescription.

I had received a notice few days ago that they have an issue with my prescription. And they want to fine me if I dont explain to them why Im claiming free prescriptions.

All I know is that I had been doing it for many years. Since my support worker at the time told me I was allowed to.

I dont remember exactly if we had to fill in any additional forms for prescription (maybe) since this was many years ago.

I dont know what to tell them.

I am not sure if this notice is not related to me sending ESA 3 form as this is so close in time.

I am terrified, not sure what to tell them.

Any advice?