Excessive data charges

i have been a loyal Cell C customer for many years. A while ago, after I renewed my contract and got a smartphone, I was debited for R1400. When I went in to question this, they checked my phone and said the settings were wrong and were autoupdating. I accepted this even though I couldn't understand how the data could jump from R250 to R1400. Since then my phone has been fine. Then last month I was debited R1400 and this months bill is R1375. I have taken my phone in and was told the Google playstore was using 100MB every 7 days, this was background information. They told me my phone was updating between 12:00 and 04:00. They checked my phone again and said the settings were right, however after setting a limit on my account I received a message saying I had run out of data- almost R100 in a week when I deliberately haven't used my phone. After phoning Samsung headoffice they told me that my settings were incorrect, despite cell c checking. I have lodged a dispute & after 4 working days no one contacted me. Today, when I called I was told the dispute had been lodged in the wrong department and I would have to wait again. I was told the error on my bill is not their problem.