We have had the EXACT same issue over the past several months, and this month is the worst yet. No increase in consumption, and we even turn our data off when we're at home since we're on WiFi (have I mentioned that I work from home?). I sometimes even turn it off when I'm away from home to try to conserve.
I turned off background app refresh and Wi-Fi assist months ago, check that they're still off after an update. Last month we were almost out of data with about two weeks left in the period. This month, we're suddenly out of data ONE WEEK into the period.
I am THIS close to contacting an attorney to see if we have a case for investigating whether Verizon intentionally uses more data in order to get us to try to subscribe to an unlimited data plan.