Stop taking my data!

Where does a persons data go? I recharged with 1G this morning and still had 50mb. I work from home and use a mifi, so my phone is connected to the mifi most of the time, even though I am not using my phone, as I am working on my laptop. Well, I go check on my data which I do regularly, out of habit and discover that I am now down to 867mb. Where, pray tell, has 183mb disappeared to??? Is MTN supplementing their "work from home" data bundles with my ****** data!!