Unfair Prescription Penalty

[greensld]

I'm new here, so any advice would be welcome.

Myself and my chemist believed I was exempt from prescription charges, only to find I wasn't in the form of a letter demanding payment, plus a £100 penalty. I sent a cheque for the prescription amount only, stating why I thought the penalty was not fair. I said that if they cashed my cheque it will confirm their acceptance that this was the full amount. They did but now they still want the extra £100. Don't know if there is an appeal procedure or if my only option is to pay up.