htc one x data question

[ahzz7319]

Ok so I'm on a pool plan of 20 gb a month and I'm currently at 16 gigs with 2 weeks left me using 12 of those gigs I use netflix a lot at my job I'm a security guard so I use it a lot but when I add up the data from the usage I get about 6 gigs but when I call at&t data usage I get the text that I personally used 12 gigs I don't get it it says my netflix used 3gig and that's the most a app uses everything else is less than a gig any ideas? My usage dates are accurate to my plan there is 6 gigs unaccounted for any help would be greatly appreciated thanks I don't know how to do a screen shot if you tell me how I will post photos thank you