Excessive monthly charge

I had taken out a black Friday deal with MTN in 2016 and renewed it every 2 years since. 2 weeks ago, I had further renewed it for an additional period of 2 years. The contract that I am on is R299 a month and purely a data contract.

This morning, my debit orders went out and MTN had charged me R1700. Upon calling them, I was told that it is a pro-rata charge for my contract. How on earth do they pro-rata R299 and get R1700? The customer care could not assist, neither could the contracts department. I tried calling numerous times and eventually got hold only to be told that the systems are offline and they can't assist anyway.

I was not told about any charges to total R1700 when further renewing the contract, neither was I sent any confirmation of the contract I had taken out despite requesting so.