Time to find the ATT SIM card and gut it from both of my vehicles.
The bbc or someone has had at least one article about a bird tracking device that operated via cellular and a sim that expected 5k or less data a month suddenly started charging gigs a month in their home continent just after the last natural looking flight of the bird ended, the ornithological society involved had a few shock bills.
As a consumer you can buy similar - I know my ISP (A&A) will sell you (quite reasonably) a sim that will drop straight onto an L2TP connection of your choosing.