excessive data usage

I am trying to determine why my data usage has spike from less than 700 per month to over 1000 being used in the first seven days of my last two bills. The equipment connected to the Internet hadn’t changed. It’s not the result of streaming or gaming because my son and I used to game daily in December. it isn’t the result of streaming because we are streaming less. I am looking for help in trying to determine why there is a spy and what device if any is causing spike.   I know the more profitable but with the bill of over $360 a month who wants to pay almost $400 a month to get unlimited when my use should continue to average what it has for the past couple of years.   looking for help in resolving the problem and not simply just pay the $30 extra.