Very disappointed

I am very disappointed with cell c, I was handed over to Shapiro sheiks due to retrenchment in 2021, I struggled to find a job, I tried to pay the amount, I finally got the job, and I paid the R15000 within 6months, now I supposed to get paid up letter I am struggling they keep on saying I am owing, R1200. this IS SO PAINFUL I STARVED MY KIDS SO THAT I CAN SETTLE THIS AMOUNT I DID now I am failing to get my letter. Even if their client Shapiro Sheiks is sending the statement that I paid in full, they still insist that I am owing. Where can I go to launch a complain? I am trying to fix my credit record, but this company is failing me.