Parking ticket advice

My son got a ticket at a local sports center that was a Pay & Display where he was part of the away team playing football. A ticket was sent to my adress and he responded with a chequer for the parking ticket explaining that he was led to belive there wasnt any charge but if there was he was happy to pay. It also reffered to his new address. He tried to contact via phone to dicuss but no number. They then sent him and even larger ticket to his new address, proving receipt of the original letter. Again he tried to contact and said it was obvoios that they wer not accpeting his cheque and offereing to pay the original ticket. but no number. Now they have put it in the hands of a debt collection company. He, and I, are pretty pissed as its impossible to talk or contact anyone. Ibe told him to go to citizens advice but wondered if the BBS had any experince? Its a private ticket btw not a council or police one.

He is an aprentice in Bristol and earns 50p and a T shirt currently.