EXCESSIVE DATA USAGE

I have a business contract with Vodacom with an Iphone 4 which I have had for a few years already. M<br> y phone account is on average about R1100 per month, from September 2014 it went up to about R1800, then R2100, then R2500 and now averaging R5500. the data usage is over R4000 per month. I have no applications open on the phone except for What's up and Facebook. I have contacted Vodacom about this excessive data usage that is occurring, but the response has not been satisfactory. They have instructed me to send a letter to them so that they can do an investigation and in the meantime my account is running up. I cannot believe that I am the only one experiencing this problem.