help county court claim has arrived

[Abzg2k19]

hi so i been ignoring letters from civil enforcement ltd since last year October after my father had a appointment at a clinic that the parking is operated by cel. it is a small car park right next to a pharmacy and dental clinic and upon entering theres a residents parking only sign but if u go to the pharmacy or the clinic they got a iPad there where you can type your reg in for free parking. my father also had a blue badge so thinking he could park free anyway he didn't thought about the parking and never saw the signs and no one in reception told him to type in his reg for free parking. after 2 weeks we received a pcn through the post i had the appointment letter,photocopied it and posted it to them recorded delivery still got receipt to prove but they reject the letter was told to ignore as you sent them a letter so they wont take you to court but they kept sending letters till this week but have sent a county claim form instead now my father was just the driver not the registered keeper any advice on a defence will be highly appreciated