unusually high internet data usage and overage charges

I saw in other threads that people were having the same problem as me, but it looks like they were helped by private messages. Just last week, I got a notice that I had exceeded my 1229 GB of data for the month. It was only the 17th of the month, but I had already used twice as much data as I typically use in a month. I worked with agents to reset and rename my network and change my password. I did look and find a few devices that I didn't know and got rid of them Even now, although it has slowed down some, I still seem to be burning through more data than would seem possible. I really need some help figuring this out.