Bad service and lies

I app**** for a month to month router with mtn,i paid R640 on the 16th of September and i was told that i will be paying in November because the R640 covers the Prorata and the month of October ,meaning after the R640 i will only be paying in November now all of a sudden they have changed they switched it off because they expect me to pay yet they said i will pay in November ,now all of a sudden they are saying i was misinformed but whose fault is it???