MTN do not answer any calls!

I received a outstanding amount letter from Shapiro Shaik for my MTN account. I paid the amount in full. A month later I am trying to get a paid off letter but they have come back to me saying that MTN is claiming I still owe them money even though Shapiro Shaik are saying my account is reflecting a zero balance and that I need to sort it out with MTN. Clearly MTN do not like employing people to answer their phones as I only get automated answers that are of no use. I am furious and sick of this back and forth emails!!!