big invoice but no airtime

I went into our local MTN store to upgrade my package from a my chat 100 to a my chat 350 so first i don't get any prorate airtime witch was ok because it was only 5 days until my top up then the 20th comes and no top up so the next day i phone the call center and the lady tells me no their having a problem the airtime will be allocated in the course of the day so the next morning i get loaded with a 100 min so i go into the store and he said that our package is showing 350 on one part and 100 on another so he logged a fault. the next day i get a invoice for R 644.39 after the lady that did our migration said my bill would be R385 so i phone once again and the lady Ref *** said she would log a fault and they will fix it .so yesterday i went into the store again and they gave me a new ref*** and its still not fixed