Was anything else connected to the wifi hotspot of your phone? eg laptops doing an update for example. But yeah 80gb is a lot, you should check the data usage settings in your phone, it should show the last 30 days and will highlight what used the data on your phone, wifi hotspot will show separately.
One other thing, has your new goodybag definitely started? It isn’t still showing as queued is it? If your old one hasn’t expired, you need to start the new one manually, which you can do when you have less than 100MB remaining.