Incorrect billing / Data account not locked

Hello Peter,<br> Earlier this year I realized that my 5 Gig data account that I use for my tablet was not locked. I paid R250/month for 5 gig but my account was running into much higher amounts. I send mails to MTN to get my account locked on the 5 gig but had no response. I went to 2 shops and they were both closed in working hours. I eventually find an open one and the lady assist me to get the data logged on 5 Gig. I felt as I have proof to show that I was trying to contact them to get this corrected that | am NOT responsible for the full account outstanding as this would not have happened if they did reply in time and assist me with the error. I have been paying my R250 every month but it is now 6 months later and they still haven't sorted this out, every time I am told that MT|N are busy with investigations. My children's accounts for their cell phones are also locked, but there was no error on their account and it has been paid in full. This is the only means that they can get hold of me from school should something happen to them. The last month we had no service at all. What should I do now? Kind regards.