Horrible service from CellC and their customer service line

I had a data sim contract with Cell C that I cancelled in 2022, after I cancelled, Cell C continued to say I have an outstanding amount owing. After a back and forth between Cell C and I, it was determined that I have an outstanding amount of R40,97 and if I make the payment the whole issue would be resolved and my contract cancelled. I paid the amount and I emailed a PoP to the collections department and I didn’t get a response. Today Cell C calls me to say I have an outstanding balance of R40,97. I told them I have paid this amount over a year ago but they still persist that I owe them. I’ve been on the phone for over 30 minutes between the collections department and the customer service department with no one willing to help except to just say I must pay. I don’t understand why I must pay again when I have paid before and emailed a PoP to which Cell C did not respond to!! It’s so frustrating!