Money always outdating

<p>I've had a contract phone with MTN for almost two years now & during this period, i've been rather unhappy with their services. I'm always getting calls from their contact center telling me about money that is owed to them. Several times I have heard this and thought it was my fault and I would pay the amount. Of recent, I asked them via email how much it would cost me to settle my account with them because I wanted to cancel my contract. I then received a quote with an amount due, which I went on to paying. Two weeks later, I haven't received anything from them terminating my contract, instead I received another call from them telling me that I stil have money due on my account. I have been the most patient with them and I'm in disbelif of the treatment i've been getting from them. How do I always have money outstanding that I don't know of? I'm extremely angered by this.</p>