Contract loaded incorrectly

Took out a contract with MTN Sandton City branch. I was with Nashua Mobile and was due to upgrade so had to go somewhere else. Went to the Sandton City MTN and took out a new upgrade. Stella assisted me and I took out a new contract which is a top up contract of R369 per month. This was in March and every month my line gets suspended and I have to phone MTN who you can never get through to the call centre and when I go into the store or phone them the stores blames MTN and MTN blames the store. <br> I have had enough of their excuses and my account has been debited for incorrect amounts every month - the last month it was over R700. <br> What must I do to get this sorted out - perhaps I should take Cell C up on their buyout offer ???<br> I cannot handle incompetency and excuses - why can't somebody take responsibility and sort this out.<br> I had been with Nashua Mobile for over 10 years and never ever ever had this problem - this makes me think that it must be the store and not the service provide??