MTN Harassment

I feel very harassed by MTN and I have been trying to sort out this matter for months now. I paid my MTN account in March at MTN westgate but my account is still in arrears and they have even handed me over to the debt collectors. I sent them a proof of payment yet they they do not consider it or they rather send me emails to say my account is still in arrears.

I need help to sort out my MTN account and I need my name to be cleared.