Why are you overcharging me?

When I got my bill for the month of June 2015 it was around R804-92. So I queried it wit Daniel (ref ***) & was told it was for smses. I argued that point because every month when my smses are finished I receive an sms from MTN then I buy more by dialling *141*2# or I buy using my loyalty points. So exactly how do I owe u for smses????? Again on the 07th of July 2015 I queried it with Marvin (ref ***) & was told that an email was being sent directly to whoever is responsible & that will speed up the process. I am still waiting. Today an sms from MTN threatening to suspend my line if payment is not made. If this is how u treat your loyaly clients then I am sorry I will not be renewing my contract at the end of the year. For now how about some feedback on my query before threathening to suspend my line??? Tried calling 808 x3 times today & no joy.