PCN Notice letters not received from U.K. CPM

Hi there, after reading through the newbies section I’m sure that my case doesn’t come up so please accept my apologies if it does and my eyesight is letting me down.

I parked my car at a Uk CPM ran car park back in April and a few months later I suddenly received a letter from their debt collectors. After speaking with the debt collectors I got them to send me through a picture of my parking and whilst I don’t deny that I was parked outside a poorly marked bay due to that being the only way to park at the time. What I do deny is receiving the two letters previous to the debt collectors asking me to pay £60 within 14 days and then £100. I have confirmed with UK CPM that they don’t send their mail recorded delivery but do record that it was sent. My issue now is why should I accept their word that these letters were sent? And why should I pay £100 more for the fine than what I should’ve paid if they sent the original letter.

Further to this, I have explained to them time and time again how two friends parked in the same car park and received PCNs but one received the initial letter and paid £60 and the other received only the second letter stating they were late with payment and have to pay £100. He is currently disputing this but I need some advice as IAS appeals have come back to my enquiry about whether I could raise a non standard appeal to state that U.K. CPM have proof they sent the letters so I have no leg to stand on.
What do I do from here as I’m sure this wouldn’t stand up in court! Even if I had received the 2nd letter and not the 1st letter I would still feel obliged to refuse this penalty charge.

Again, apologies if this is going over old ground but as you can imagine, being bombarded by debt collection letters is quite stressful!

Regards