excessive usage of data on my Mobile phone

I have recently asked Vodacom to look into the fact that my phone,use an excessive use of data.an I was adviced and went through my phone setting with one of the consultant,but still the problem continued so I then contacted Vodacom.an enquiry was opened an they told me that its facebook cause I switch my data off when ever I'm busy n not using my phone.so I went ahead and log out of facebook as I was adviced to log out everytime after using Facebook.on Tuesday I purchased 100Mb to monitor the usage.to my surprise this morning data gone.in actual fact I had used 650Mb of data in less than 10 days.during our recorded phone call with one of the consultant I think he said his name is Mark,he specifically told me there's nothing Vodacom can do to assist me in looking where the problem could be.