extreme data usage

My husbands personal cell data jumped from .39 gb used to 1.67 within hours.    Yesterday We recieved an email that said we used 50% of our data at 12:30pm and by 4:30pm we recieved email that said we used 100% of our data.  We called xfinity and the lady tried to tell us that is was the apps he had open and the internet. She wanted him to turn of Cellular data.  But the thing is he never left the house yesterday so he was on our wifi and there were no chances made on his phone that would cause issues in one day.  He works from home, has a work phone assigned to him, did not have internet problems on his computer all day.  Also, I was home all day and my data useage stayed at .19 gb and still is at .19gb.  The month for useage is jan 24 - feb 23 and we rarely go over 1 GB every month and if we do it is at the end of the month not in the middle.  This huge spike does not make sense.  We have done nothing different than we usually do.  No matter how much I tried to explain the facts I do not think the lady understand that the issue was not on our end.  At this rate by the end of the usage cycle (according to Xfinity) we will probably use 3GB of data.  The woman ended up giving us credit for one GB but we will still be paying for 1GB of data we did not use.  It would be greatly appreciated if someone could explain this or if they have had issues like this.