If this letter reached you at your current address, then a previous letter should also have been received. This is the letter sent at the "Compliance" stage, when the bailiff fee is £75 plus the council debt of the amount at the Order for Recovery stage. The letter you have received is the one sent at the second stage of enforcement, the "taking control of goods" stage. Yet you don't mention this letter at all ? So did your receive such a letter ?
Here are the relevant regulations :-
These Regulations make provision for recovery of fees and disbursements from debtors by enforcement agents in relation to the procedure for taking control of goods under Schedule 12 to the Tribunal...
See Regulation 5 and Schedule 12
The compliance fee is £75, and the attendance fee £235
The only way to revert the process back to the PCN stage is to submit a Statutory Declaration or a Witness Statement. Which one depends under what legislation the PCN was issued. Because you are way out of time to submit either of these, you also have to submit separate form to request that the SD or WS form can be submitted Out-of-Time. Whether you've paid the bailiff or not, it has no relevance or input, to the WS or SD process. With your late update of your V5C, you'll need a very good story to explain things.