Disgusting

I have had an account with Dona Claire for many years. I always use the 6 month repayment option. I paid the account up in 2020 and only started using it again at the end of February 2022. I received an account on 18 March 2022 which was dated 12 March 2022. Received a call from the head office on 2 April requesting a payment. I made a payment the very next day. I received an account on 21 April reflecting a balance of R32.00 which is charges for 1 phone call, an SMS and interest. Really since when are these charges being added. DISGUSTING to say the least. Imbeciles working in the accounts department. Since when did the terms and conditions change. As far as I know no interest is charged on a 6 months payment option. I need an urgent explanation.