Update: Got the car back. With working heated seats and...a passenger seatbelt warning chime that won’t stop. Even with nothing in the seat.
I guess the heat pad in that seat is triggering the weight/occupancy sensor. I left the parking lot of the upholstery shop, went to get gas (car was almost empty) and went right back to tell them the issue...which they should’ve noticed before telling me to come pick up the car.
They told me to bring it back in the morning so they can fix it. I’m not sure how they’ll fix it, but I refuse to drive around with the empty passenger seat buckled forever.
I’m annoyed, to say the least.