NUDEBT HARASSMENT FOR AN INCORRECT MTN BUSINESS ACCOUNT

I have send emails with proof on the outstanding balance on my account to MTN collection company NUDEBT. What is wrong with these people. They have the incorrect amount and I have been trying to sort this out with them and MTN business for the a few months. Emails and correspondence was send with the correct amounts and details but with absolutely no success from both mtn or nudebt. This nudebt just keep on sending demands and the still the incorrect amount due. I am finished with the lack of stupidity from these people. I HAVE NOT RENEW ANY CONTRACTS WITH MTN ON THIS BUSINESS ACCOUNT BUT YET THEY ARE REQUESTING AN SHOCKING AMOUNT OF OVER R32000 vs the correct amount of under R3000.