Parking Dispute

[Guest]

I parked on a National Trust car park.On departure the parking camera/refused to accept my money,I assume "Park with Ease",who operate on behalf of the National Trust,have video evidence of my attempts ,and my wifes attempts,and onlookers attempts to insert cash into their machine .I left but on receipt of a demand for £110 from "park with ease" I sent a cheque for £5 which I considered to be fair payment for the hour or so we used the car park.This was returned.I then get a letters from "Equita" which tell me that they have refered the matter back to Park with Ease with a recommendation of Enforcement/Litigation action.What is my best course of action? sincertely Alfred Owen