Check all under hood and under dash fuses with a test light or multimeter.

There's also several TSBs regarding seat heaters inoperative that mention software updates.
If you haven't been to a GM dealer recently, there is a good chance you need the module's updated. At the very least they can check to see if you have any Diagnostic Trouble Codes (DTCs) in the seat control module.

Happened to my Tahoe. I found the plastic kick panel by my left foot was rubbing into a wire harness that comes through the firewall and goes down under the driver seat. Repaired all the wires it rubbed through, taped it heavily and zip tied the harness out of the way of the panel. The fuse for it is the MBEC 1 fuse under the hood. Hope this helps someone out there lol.