I do have echos and Ring cameras, but they are not new. They've never used this much data. Confusingly, Friday, Saturday, and Sunday when we were home we used 50-100GB / day. That makes sense if we were both streaming all day. Monday, when we were not home, we used about 17GB, which also seems reasonable. But then Tuesday, Wednesday, Thursday when we were also not home, we used 250-350 GB / day, which is outrageous.
I double checked and there aren't any open networks. We have a secure password and no kids, so it seems unlikely that there was any outside access.