Your only avenue now, (with bailiffs already instructed), is to submit an Out-of-Time Witness Statement, or Statutory Declaration to the Traffic Enforcement Centre. Which one to submit depends on what Act of Parliament the original PCN was served under.
So please post-up the documentation. Redact only name and address.
The bailiff visit will add another £235 onto the amount owing, so if you can pay before he turns up, you'll avoid this, (hopefully !).
Paying the bailiff has no effect on whether your OOT submission above is accepted or not.