Cannot make any calls for 3 months

I upgraded my contract with MTN in May ever since then I cannot seem to make any calls, I've been to the store numerous times they wasted 2 hours and more figuring out what's wrong but they have no idea! I have called the call center and no one knows what's wrong as everything is perfect on the system they say. I even did a sim swop and still nothing changed, I cannot make any outgoing calls with my SIM card, my phone is not the issue its just my SIM card, it does not work in any cellphone! I'm so frustrated to be paying every single month for something which I cannot use and nobody at all can even help me! I hate MTN as all ur staff seem to have no knowledge of anything, I really regret upgrading my contract with MTN even though I've been a client for about 17 years now! MTN is by the far the worst company in South Africa and I will make sure once the contract is expired to cancel all my other contracts with MTN!