Admin errors do not invalidate parking tickets.
Was it private land or Council - real tickets that you have to pay will have the address of a court on them and will say 'Penalty Charge Notice'. Civil ones have the address of a private company and say something like 'Parking Charge Notice'.
If it is a private ticket, bin it. You do not have to ring them or quote legislation - just ignore it, along with any letters that follow, no matter how threatening they appear. Entering into discussion with them just shows they have a 'live one'.
Private tickets are based on contract law. To enforce them, they must prove there was a contract between you. Also note any contract is with the driver - NOT the registered keeper. Do not admit to being the driver under any circumstances.
If it is on Council land, pay up.
With regards to the Mini, in the previous response, I am guessing that was a private ticket. You would not get away with that if it was a proper parking ticket issued by a local authority.