I don't think the OP's concern is opening post, it's whether they're likely to have bailiffs turning up on the doorstep. OP, pl confirm.
Others have more knowledge, but as I understand it, unless the sum outstanding meets the High Court enforcement threshold then 'enforcement officers' aren't engaged. A single parking charge would not meet this threshold.
We have had a PCN for previous occupants for an incident in 2019
When exactly in 2019? I ask because the limit for bringing any legal proceedings in this matter(alleged breach of simple contract) is 6 years and once this deadline has passed you should be free from the nuisance.