charging for "free" upgrade

SO first MTN called to tell me my number has been upgraded for free to a bigger packages for the rest of the remaining time on my contract ; when the bill come that charged me for the "free upgrade" after i complained they cancelled the upgrade and refunded me ; the again my October invoice come and again i was charged for the migration ; the free upgrade that i constantly asked are you sure nothing is going to be extra keeps costing me money? this is the 3rd time this year.

MTN is a ***** and just adding to my bill.