We had prepaid mobile with Boost and Verizon. Used the phones monthly and each had 3 GB data. With new phones on shared Verizon Plans we used 3 times as much data!! Seriously?? How are they gauging the data usage?? And why so much higher with Verizon plan not prepaid?
What type of devices were you previously using? Were they 4G? Prepaid up until recently, utilized the carriers' older 3G data network. 4G was reserved for postpaid customers. 4G IMO seems to use more data than 3G. Also, depending on the device, background data can use data unknowingly to the user. Have you used settings to see if an app or process is consuming large amounts of data?