I’m pretty sure (99%) that there is no offence committed by using these ‘back doors’. Whilst it is discouraged, no specific legislation exists. The only potential offence is the civil one of trespass. Personally I’d just ignore the parking charge. This is not particularly good advice, and certainly risks it going wrong, but it has worked for me in the past, more than once. The way I see it is that once they have a proven interaction with an actual human being, it becomes worth their while to harass you, because they know that statistically, people are likely to cough up for an easy life. No reply and they give up quickly as I bet they often don’t manage to open dialogue due to incorrect details etc, and statistically these cases aren’t worth investing the time in. Like I said, NOT good advice, but it definitely has a good chance of working, especially in your case whereby if it DID go to court they’d look pretty stupid anyway.