There are 2 maroon cell antenna door plugs, one at drivers mirror, one at passengers mirror.
I prefer to pull the MCU slightly out of the dash and disconnect the main maroon cell antenna plug (upper right, near the glovebox) right from the back of the MCU. I feel like that's a better signal prevention method, just in case they can pick up signals thru the length of the cords, like how headphone cords become the antenna of a pocket FM radio.
Which vehicle model do you have? A 3 might have supercharger-to-car direct communication to disable supercharging, but my older S does not have that, and is completely isolated since I disconnected cellular. Try this method below, and let us know if it works