I parked for 45 mins in an off street car park in Frome. I

I parked for 45 mins in an off street car park in Frome. I looked for nearest in sight pay and display machine and paid for 1 hour. I have the ticket confirming this.Two weeks later I received a PCN for non payment. I appealed and sent copy of parking machine ticket. My appeal has been rejected as "not valid at this location". I saw no other or closer machine. Their letter says signs say "phone and pay". I saw no such sign. Would revisit location to confirm but it's more than 100 miles away. Should I go to POPLA?
JA: Because traffic laws vary from place to place, can you tell me where this is?
Customer: Frome, Somerset
JA: Do you need to appear in court?
Customer: No
JA: Anything else you want the Lawyer to know before I connect you?
Customer: Adjacent signs said "Euro Car parks" whose ticket machine I used, but PCN is from Civil Enforcement Ltd. No clear sign that the part I parked in was not part of Euro Car Parks; I've checked Google Streetview.