There are a number of things that can all of a sudden start using a LOT of data. Someone in these forums several months back had a similar issue, then found he had installed one drive on his phone, and it would sync to one drive and upload from, his phone the entire phone, and use close to 100gb each time. if you did that with several devices, well, adds up quick.
Also, while streaming habits may not have changed, the resolution of the streaming MAY have, and while standard HD uses, 2.3 to 2.8gb an hour, 4K tv uses 8gb an hour and more. 2 movies in an evening, could go from using 10gb, to using 32 gb, and if you have 2 people each on their own tv, that could easily double from instead of 20gb, to using 64 gb and that's just for 2 tvs each watching 2 movies at 4k. it doesn't count what devices like tablets or phones, computers, and more could be using.