done this a few years ago . go onto equifax and it lists all your credit agreements over a time, give the creditors a call doesnt matter if your finished with them or not, whether your in arrears etc, fact is they have charged you PPI, they are in breach of the law, they are legaly obliged to inform you if PPI is/ was on the account if so ask for a claim form from them ,fill it in , get it back to them and normally within a few months they will contact you with an offer or in some cases you will get a cheque directly . Using a PPI claims company the procedure is the same only they do the contacting credit companies and charge you a % sometimes up to 30% which can be a substantial amount. Good luck its your Money.