Free Traffic Legal Advice

Sorry for the formatting, I'm typing on phone. I'm also dyslexic as hell (which is why I got into this mess).

I stayed two nights at a premier Inn in London. I used their onsite parking and paid through the appointed app (YourParkingSpace) for 2 days of parking.

A month later I received a PCN by post from the parking company (ParkMaven Ltd) stating I had parked without paying and now have to pay a fine.
I was quite shocked at this and appealed right away with screen shots of the app showing I made payment for the two days I was there.

I then received a second reminder by post about the fine. This was dated before I sent the appeal so decided to ignore it.

I received an email reply stating that my appeal had been granted. There was an error inputting my registration. An o was entered instead of 0.
Great I thought, case closed and I'll move on.

I then received a third reminder letter by post that's as the same as the original. It was dated before I received the appeal so ignored it and moved on.

A month later I receive a debt collectors (DCBL) letter stating the the fine has now been passed on to them and they want payment at an inflated price.
What the hell???

I contacted the original parking company demanding to know what happened. I provided evidence that I originally paid for parking and the fine had appealed. The parking company now states that the fine that was passed on to the debt collectors is for the second day!

It turns out they sent two fines for both days! The second letter i received was a fine for the second day, they had fined each day as sperate. I just didn't notice different reference numbers assumed it was all the same fine.

I asked for this fine to be scrapped for the same reason as the first but they informed me that my right to appeal is now over and I would have to contact the debt collectors.

I am now at loss as what to do? How did they not cancel the fine for both days?
Do I contact the debt collectors? I really don't trust them to even care.
Do I just make a firm stance with ParkMaven and tell them their system is the issue as i notified them of original payment for both of the days.
Is it worth me contacting a solicitor?
My fiancé would rather we just pay the fine as she's worried about Bailiffs at our door and our credit score being hit.

Any advice would be greatly appreciated.