MTN BAD CUSTOMER SERVICE

I have been a customer of MTN for many years, I have a contract with them for R350 per month, I eft the amount every month, no problem. Now all of the sudden they have suspended my account for non payment. I sent all proof of payments to them. The amount they say I owe them is less than my contract fee. On my December statement is shows I only owed them R00.20c which is incorrect, but I still paid my R350. I have asked for a detailed account showing all payments that have been made. I simply refuse the pay the amount as I know and have proof that I paid them. They are just so useless. I just don't know what to do anymore.