Huge increase in data usage

The last two months we have seen a huge increase in our monthly data usage. We normal would average around 700gb a month but starting in May and now in June we've gone over our cap. We haven't added any new devices in the house nor have our normal streaming/gaming/browsing habits changed. We were even on vacation for a full week in May and still went over. I've checked to see what devices are connected and no unknown devices are connected. Does anyone have an idea what could be happening?