Double charged and no communication with me.

I upgraded my phone on the 17th of April 2015. On may I was billed R1010 . In that invoice they added upgrade fees and I was told that the following month the amount will be less than that as my agreement with them said I'll be paying R700 for the new phone including insurance. This month my invoice came, my bill was R1236. The insurance deducted 3 times, I was also charged for promotional services , I'm also still being billed by Nashua mobile for the 3rd time now. I have complained several times at MTN Mimosa mall but no one seem to take this seriously. Even now as I'm currently writing this email. My phone is locked, all that they can say to me is that we are on Strike and can't help you. For 3months I've been paying double the agreed amount that I was supposed to pay and they haven't even refunded me for those months. I'm so sick and fed up with the service that MTN is giving. Even after an upgrade I'm paying double amount for Nashua mobile and MTN... I'm so annoyed by their service towards us as consumers.