Head over to PePiPoo Forums, register, and post a topic there. Far more specialist knowledge about Private Car Park Parking Charge Notices, than we have here.
Before I proceed, I'll stress I am not a lawyer. My knowledge of private parking tickets comes merely from extensive reading on the subject online. Parking Charge Notices (PCN) issued in private car parks are one of the greatest injustices against motorists currently allowed.
What I will say though is this car park is on railway land where railway byelaws almost certainly apply and the Protection of Freedoms Act 2012 doesn't. That means only a magistrate can impose any form of financial penalty for an alleged breach of railway byelaws in regard to parking. That doesn't stop
APCOA▸ trying to claim you owe then a Parking Charge, nor does it stop debt collectors trying to enforce an alleged debt. Their alleged Parking Charge can only be enforced in the County Court as a civil debt.
I fear you may have identified yourself as the driver on the day in question. Only the driver can be liable under Railway Byelaws. APCOA and their debt collectors may try and claim there is Keeper Liability under POFA 2012. That would almost certainly not be the case as the land in question is not relevant land for POFA 2012. If you've not identified yourself as the driver keep it that way. Refer to the driver in the third person in all correspondence, "The driver did this, the driver did that..." etc.
It is unlikely that a Railway Byelaw claim can be made against the driver in the magistrates court in this case as the claimant has to lay particulars within 6 months of any alleged contravention. So that, at least shuts down any criminal sanction. However, that doesn't stop either APCoA or Debt Recovery Plus threatening civil action against the registered keeper in the County Court. Whether those threats are justified when the alleged tort is almost certainly against the land owner (GWR on behalf of Network Rail) is an exercise for those with greater legal knowledge than I. Such people contribute to PePiPoo.
The first thing to do is appeal in writing to the car park operator. A simple "the charge doesn't reflect your losses" appeal will suffice at this point. Appeal in writing regardless of what they say about timescales. Keep copies of emails and, if using the post, obtain a free certificate of posting at a post office for all letters sent. In that appeal you need to state that should your appeal be unsuccessful, or simply not allowed because it has timed out (time limits are totally arbitrary, set by the operator themselves), then you require the dispute to be settled by an Alternative Dispute Resolution body. This could be POPLA or the Consumer Ombudsman if POPLA won't help. This is so you appear reasonable should the matter go as far as a County Court hearing. It won't look good to the judge if the claimant(s) has/have not attempted to resolve the dispute before court.
So, head over to PePiPoo, register and post a topic on their 'Private Parking Tickets & Clamping' board. It'd be helpful if you can include uploads of any correspondence (redacted of personal information) you've received from APCOA and Debt Recovery Plus.
Finally, don't make any more phone calls to APCoA or Debt Recovery Plus. All correspondence should be in writing/email so you can keep records. And best to run all your outgoing correspondence by the folk at PePiPoo before sending it.
http://forums.pepipoo.com/