Co-operative Bank CCA non-compliance

I've recently received a letter regarding my loan account from the Co-operative stating that they have previously provided me with information which did not fully comply with the CCA and as such I am not liable to pay interest of default charges for the effected period (Feb-Oct 16) and refunded just under £250 of interest.

A week later I received a further letter stating that they had identified further issues with my account and as such they will not charge any further interest on the loan.

Over both letters, they haven't given any further information except that it didn't comply with the CCA. I've called up the number they provided on these letters and they stated that it's relating to Notice(s) of Sums in Arrears and Annual statements and that they are charging no further interest as they are unable to make my account 'compliant' with the CCA. I asked how they are unable to make it compliant and they couldn't answer, instead stating that they will send a letter out in 10 working days.

Obviously no further interest is of massive benefit to myself, however something doesn't quite sit right that they cannot give me full information as to what is wrong with my account.

Anyone had the same or got any further information?