Account Billing - Ref number ***

Yesterday Cell c phoned me to say that my account is over R4000 for end October. I was so shocked and speechless. I explain that every month my account is not higher than R700.00. this person said to me that it is the internet and I explain that I only use emails and whats up on my phone NOTHING ELSE. I've got a samsung galaxy S5 for over a year and this is the first time that this hapens to my account. this person said to me that the data is running at the back ground and they cannot help me so see who took all my data, all the data was running during the night that I was not aware off. I have ask to email me my new statement and I received last months statement. My ref number is ***. and yesterday After I spoke to cell c they suspented my line and I cannot make any calls. that I think is ridicules for I am not behind with my account and I have a business to run. This morning I spoke to Pulani and he was not really very helpful for he also said that they cannot see who download all my data and he says that I must pay 50% of this R4000 to activated my account. please cell c sort my account out. I need my phone. stil waiting for someone to contact me.