HELP PLEASE

I downgraded my account 08JUN instore at Bayside. I got charged my old contract rate for JUL & August. It looks like they changed my contract 2 days ago - who knows? My billing cycle is 12th of the month, yesterday while I am talking my phone cut off saying my airtime is finished - 100mins. Which is impossible if it started on the 12th. I have been phoning customer service, been on the line for more than 35mins I am still holding. Spoke to 2 different people, the first one was very lovely gave me reference number - but told me it can take 2days to sort out the airtime story ref: *** , The 2nd lady in billing just told me she can't help she has to put me through to Customer service again and I kept telling her, they can't help me either they said I must speak to billing. I then asked to speak to a supervisor and was put back to customer service, the lady answered listened to my story and put me on mute I pressume as I cannot hear anything but the call is still ongoing - so she can probably hear me who knows? This is really frustrating. 1st I did not budget being out of work for 5months to pay JUL & AUG that amount. 2nd I have 3 kids in 3 different schools I cannot not be able to get hold of them because I have no airtime. I have been a customer of MTN for MANY years and once you have a problem no one can help you! I am still on mute with this call its not been 40mins..........