Wrong debit amount by MTN

MTN is trying to **** me please help these guys from Mtn called for upgrade then we agreed to R300 for contract but when the lady sent me the debit autho via my bank app to confirm the amount was R6800. I rejected it now it keeps on popping up on my bank app.

Why Mtn is doing this while we surrounded by ****mer who robed us on daily basis.

Regards, Y Siyotula