man robbing me once again!!!

On the 12 May 2020, I received a bill for R1200, saying I'm overdue for 30days I never ever missed a payment even during this tough times.... on the 3 May I upgraded my bill was supposed to be about 730... mtn was to change me double the installment... what if I don't have the funds to pay this... !!! *****ing fund during tough times.