Frustrated

On the 27/05/15 I went into the Longbeach Mall Branch of MTN. I had previously spent the best part of 3 days solid trying to contact mtn via the call centre, with no answer, which is why I went into a branch. The branch were extremely helpful, I was due an upgrade at the end of Jan, & I wanted to down grade to a lower package. The assistant helped me & explained that I would still have to pay the usual R800.63 odd at the end of June as they bill in arrears & the new billing of R80pm would kick in end July, she made no mention of any outstanding amounts due, I understood & signed. The downgrade was done successfully, except on the 30/06/15 I was billed for R2957.24 I once again could not get through to the call centre at all & went into the same branch where i was advised they were offline and could not assist me in finding out why I was being billed this amount so I stopped the payment. Subsequently my bill for July is R338.57, I have spent days trying to get hold of mtn with no ans ever. The branch have advised that they cannot assist as they can't see the bill for R2957.24 on their system. It is nearly the end of the month again and I need to sort this out urgently now