These unregulated private parking firms rely on the recipients of their Parking Charge Notices (PCNs) being low-hanging fruit on the gullible tree who can be intimidated into paying up out of ignorance and fear. The first sign of a gullible recipient is when they refer to a PCN as an "offence" and/or a "fine".
I will give you £100 for every occurrence of the word "offence" or "fine" you can show me on any correspondence from them. A PCN is simply a speculative invoice for an alleged breach of contract by the driver. No offence and no fine.
Now we must first establish why you may not have heard anything about this until now. In the majority of cases, it is because at the time of the alleged contravention the Keepers address had not been updated after a move. Many Keepers don't realise that updating their drivers licence does not automatically also update their V5C.
So, before we move on, is your V5C up to date with your current address? Was it up to date with the correct address on or around the end of January, beginning of February 2024?
That letter is only a reminder that their speculative invoice has not been paid. As you know nothing about that invoice (PCN) there are some steps you can take. However, please confirm whether the V5C was up to date with the correct address where you were residing at the time of the alleged contravention.
When you've done that we can proceed.