Facebook not entirely free

Hi Cell C<br> <br> I would like to know what the limitations on free Facebook is. I have an app that tracks my data usage on my cellphone..<br> Data usage for the month so far: 263MB<br> Data usage for Facebook: 103MB<br> <br> I am on the 1GB package and get 512MB data and for the month so far I have used 210MB data.<br> Basically what it comes down to is that I have been charged 50MB 103 -(263-210) for Facebook data when it should have been free.<br> <br> Please can you explain this.<br>