PSD calls???

We recently noticed that our one contract has been billed with larger and larger amounts. Today I went onto MTN ACTIVE and saw that I'm being charged Over R1500 for PSD calls?? I looked back and I see the problem started in my April account. I on a MyChoice 200 contract and we were told that it works exactly like a Topup contract and we wouldn't get any nasty surprised. I see my calls are also being billed extra instead stopping calls being made once my minutes are finished. This is not what I signed up for MTN. I can't get hold of anyone on 808 and no one else can help.