Data has dissapeared

I have a 3gb data package , in virtually one week my remaining 1.5gb has been depleted when I have hardly used the internet. My wife has a contract with another provider with much less data. She uses her phone / facebook / WhatsApp etc a lot more than me and she still has a fair amount data left for the rest of the month even though her data package is less ??<br> A lot of people are complaining about the same issue.