MTN Bills without Invoices at Rediculous Rates

I subscribed to an MTN data contract (without) device in April. Have been using the sim in my router. I have not received a single invoice from MTN since then and for the last two months they have invoiced me at four times the contract rate!!! I can't reach them telephonically either, have tried calling multiple times only to listen to their stupid prerecorded message and song and for them NEVER to pick up. I can't register online for my account either as they want to send you a one time pin and the sim is not in my phone. And when I do put it in my phone, then I can't complete the online \send the one time pin"request as the sim is in my phone not the router. Catch 22!! All I want is my invoices and a refund for the excessive billing which is impossible!!!"""