Yes have catalogue, and personal account, but not for much longer. The 'charges' are the interest rate payable on the outstanding amount on the account, called 'the credit charge'. Like you I didn't realise that such a high interest rate was to be charged. I have just checked the reverse of my last statement, on which it says 'the rate of interest charged will be provided upon request, together with an explanation of how it has been applied to your account'.
That's not a lot of use knowing, when a person has already entered into an agreement to have a personal account. As you point out, over half of the monthly payment is for the credit charge, and less than half left to reduce the outstanding account. Being wise after the event is not a lot of consolation, but I am reducing my account to zero as quickly as possible. Best wishes. Schutz.