I expect there's some people that haven't claimed back ppi they did or didn't think they had yet.
I called a reclaim company recently on the spur of the moment as barclays said I never had a loan with them. The reclaim company has now found 23 instances in my name and so far 5k has been paid back.
Reclaim companies do take a % but if you've not got the time or effort for this a 10 minutes phone call could be good for you.
For store cards you don't even need account numbers and all I had was 1 account number from the bank...