Finance Charge on Credit Card??

I have had a credit card account with ABSA for almost 3 years now and have been a very happy customer until I decided to settle my account in full in February 2024. I had paid everything off and by the 2nd Feb, had R0.00 outstanding balance. I have not used my card deliberately as I was saving it for emergencies only but to my surprise, I receive a statement that says I owe R251 in finance charges. What are these charges for? i understand monthly charges such as Credit Life Premium, Admin fees and Facility service fees but they are separate from this Finance charge thing. I tried calling support and spoke to Theresa who advised me that the charges are for interest. She could not answer me when I asked her for what interest as my account has nothing owing because i paid everything in full. Her last words to me were "I will transfer you to the relevant department..." the she transferred my call back to the same queue I came from to get to her. What is this fee? I need someone from Absa to call me and tell me what am i being charged for on an account that is paid in full and not owing anything or I will be forced to cancel my credit card with them.