they are still liable to repay you the monies they have unlawfully added to the account.
They may well have sold the debt on for a pittance and the money they owe you is far more than they ever had in the first place.
TOUGH. that is their problem.
They will of course tell you that they sold it on so they don't owe you- rubbish.
Again, read all about it.
the court fee for £8k is £455 or less if you go online.
If you are poor there is a form you can fill out and get a remission of fees.
That will bring the cost down to zero if your circumstances are that bad.
You don't have to be on benefits but if you are it is easier for them to check your entitlement to the remission.