Sick of Billig Errors

I was a very happy cluent if Nashua Mobile for 20 years - even since Mtn took over I have had billing ptoblems - I have called every month , but am billed incorrectly the following month again . This month as soon as I received my invoice I called , was told the problem was logged and that I should pay my usual amount which I did at Mtn Canal Walk - they checked fir me and my query was been sent to different departments- well , my cell fone was cut off yesterday - I was cut off over 30x when trying to get hold of the call centre - finally got thru , problem logged again - my phone is still not on - I have emailed and tweeted - no response at all from MTN - this is really bad service - MY PHONE Has been cut because of your incompetence!!! I am sick of this - what more must I do -