Please read this and then post a suitably redacted photo of both sides of the Notice to Keeper (NtK). Regarding the PoFA deadline regarding service of the NtK, it refers to it needing to be "given" within 14 days of the alleged contravention.
A Notice is deemed given, two working days after the date it is issued (not the contravention date), irrespective of whether it actually arrives later or not, unless it can be proven to have arrived later. If the PCN is dated only 7 days after the alleged contravention then it was deemed given two working days later, which is more likely than to be within the 14 days stipulated by PoFA. Without knowing the actual dates, it is difficult to confirm especially if it was issued around the Xmas holiday period.
You mention that DCBL have now been in touch which suggests that any appeal period is no longer possible. DCBL must be ignored. They are a useless debt collector with no power to do anything except try and scare the low-hanging fruit on the gullible tree to pay up out of ignorance and fear.
The hotel must be pressured as far as possible to get the PCN cancelled if they are the contractor for ParkMaven. The only way you will get to see any contract between the landowner and ParkMaven is if they issue a county court claim and it goes all the way to a hearing where you can require ParkMaven to reveal their contractual right to issue PCNs in their own name.
However, if it goes to a county court claim, there is very little to zero chance that it would ever get as far as a hearing as they are likely to discontinue before the hearing fee has to paid by them.
When you can, please show the NtK and if you get a Letter of Claim (LoC) come back and show us.