Worst Ever Service

I had a MTN Contract with Nashua Mobile. Last year November 2014, it change over directly to MTN. 20 December 2014 I went to upgrade the old contract of R800 to new contract directly with MTN for about R280 at the MTN branch in Tygervalley. My old contract was immediately cancelled, but since then they never could get my billing on the new contract right. I tried to phone customer care, you can never get a hold of them, the number not available. The branch in Kuruman can not see the contract on the system to help me, because of it being a previously Nashua Mobile contract, even if I had done the upgrade directly with MTN. They have to lodge a query and still after three times MTN can still not get it right, they still bill me the old contract amount. I have complaint about this on an email to customer care, but now I received a letter to threaten me that if I do not pay the account up to date, MTN is going to cancel the contract and I will still be responsible for the early cancellation fee of R5400. This is the most worst and frustrating service ever!!!!! They can not get it right, now they threatening me!!! Wake up!