MTN unwilling to help!!!! Can't make phone calls

I bought a MTN contract a Sky Lite, the contract advertises unlimited talk time, now I can't make phone calls, then the useless call centre tells me that I signed for unlimited talk time to MTN networks only, they don't have any proof that I have signed for that but their arrogant staff is unwilling to help. Where can I go to help from this useless service provider??