Clearence letter from cell c

Cell c services is very bad, i took a cell phone contract with cell c in June this year .. then on the 4th of July 2022. I decided to terminate contract the i was told to pay R 11 452 .00, i paid this whole amount and i have a proof of payment . I have been trying to call cell c to give me a clearence letter to show that my contract paid up I was given a Reference number of my case and e very time when i call them they keep on saying they doing investigations and im waisting my time and airtime im calling every day using my airtime and no help And the destroying my credit profile i can not qaulify for any credit where ever i go they tell me im owing cell c 11 452.00 Please help me to get my clearence letter.