Data always depleted

Between the 14th and the 20th, my 20gig data bundle for my wifi is always depleted.

I browse Instagram maybe once every 2nd day, Facebook maybe once a week. I'm on works wifi during the day or guest houses wifi at night.

I don't download movies, maybe an occasional game or album.

Which would never amount to 20 gigs.

There is always a data issue every single month, no matter what restrictions are put in place or data monitoring apps are loaded.

20 gigs use to last 30 days easy, now 14 days it's gone.