HUGE bill, no response to enquiries!

I received a bill of more than R2300 this month. My bill is always around R650. It says it's for internet - and most of the money from the last two weeks in April. But my phone says I used 888mb of data for the period. I have sent three emails to Cell C, and have not had anyone phone me or mail me back. My bill is now due and there is no resolution. PLEASE can someone check up on this and get back to me.