Wrongly issued Parking Charge Notice

Hi everyone, looking for some help here. At the end of January I parked in a privately owned car park, and I paid the correct amount of money for the time that I stayed there. A few days later, in early February, a letter was sent to my address issuing a Parking Charge Notice, incorrectly stating that I hadn’t paid for my stay. Unfortunately I was away from my home address for all of February as I have been staying on my narrowboat, and only found out about this letter a couple of days ago, meaning it is now too late to appeal.

I sent them an email a couple of days ago with a screenshot of my bank statement proving that I paid for parking - I said that I was away from my address so I didn’t see the letter in time to appeal through their usual online process. They’ve sent me a reply saying I need to prove I was away for the whole of February, and I’m not quite sure how I’m supposed to prove it? I was just on my narrowboat, I wasn’t out of the country or anything so I don’t have any tickets/bookings to provide.

Anyway, I just wanted to know what my options are here. This is causing me unnecessary stress as I paid for my parking and they are the ones in the wrong, yet they’re treating me like I’m the inconvenience?? Is there any way of me not having to pay this? It seems completely unfair as I paid for my parking and it’s their mistake.

Thanks in advance for any help.