Incorrect billing - extremely overcharged by MTN

I have a home router with mtn and it have been going well for some time. Until, to my surprise, I was hit with a bill of almost R1500 for the month of November and I usually pay R295 every month.

December they went on to charge deduct R538 instead of the monthly amount of R295.

Even when I open your app, nothing is working.

I tried contacting your helpdesk to no available, fix this issue please and while at that cancel this contract asap!!!