A classic case of the low-hanging fruit on the gullible tree being plucked off and scammed because they paid up out of ignorance and fear.
What is not clear from all the above is if the PCN was paid (completely unnecessarily), do you have proof of payment? If so, on what basis is DCBL claiming that there is a debt owed to I Park Services Ltd?
As already mentioned above, DO NOT enter into any communication with DCBL or any other debt collector for that matter. Debt collectors are powerless except to try and persuade the low-hanging fruit to pay up, as mentioned, out of ignorance and fear.
The problem here is that the PCN has been paid and so that money is gone whilst I Park Services laughs all the way to the bank. Paying the PCN is tantamount to admitting liability when all the Keeper, the person who received the Notice to Keeper (NtK), had to do was deny liability without identifying the driver.
Anyway, I will place a £100 bet that no debt claim will be filed under the Simple Procedure in Scotland for a single PCN. There are many reasons for this but I am confident to make the bet, if anyone cares to take me up on it.
You have the option of completely ignoring everything that you get in the post form now on and this will wither on the vine, or you can try and waste your time and effort communicating with any of these companies, for the same outcome. I would advise the former is the easiest option.
As far as the money wasted on paying the PCN in the first place, I'm afraid that has gone to fund the scammers. Hopefully a lesson has been learnt for any future PCNs should not be paid until the Transport (Scotland) Act 2019 introduces a keeper liability scheme.