MTN A BIGGEST **** IN TOWN

Mtn a biggest ****... i have a contract that's ending this month, i have had this contact for 24m paying 278 on 120gb, to my surprise i received a message towards my payment date that i will be billed/debited R729.50 of which i couldn't afford and didn't sign up for and is also not on my contract and didn't budget for such an amount. I went to a store where i was told an agent subscribe me to some plan i wasn't told or agreed on when i called in to check if i can upgrade. I later logged a complain and was told the amount is for month to month plan as the plan i joined was on special, but it was however not stipulated in the contract... this will humongously affect my credit score and cause me financial and emotional suffering- I CAN'T AFFORD TO PAY THAT AMOUNT