Ok where is my data going

2 months ago we used up all of our data in 3 days while only checking email I called to get a n explanation as the most we had used before was under 20g I have a 60g plan. we are self employed gone all day and we live over 2 miles to the next house have password on our system. the explanation was someone from far far away was getting our data. Last month I checked it regularly and we used under 10 g no difference in the way we used the internet. Now again this month over 53 in 8 days and we haven't even been home much whats up anybody else having these kind of problems?