Without notifying the dealership, I would (as mentioned already) download the service manual, relinquish a copy of the SKREEM removal procedure for yourself. Then (in writing) have the dealership explain how they removed the SKREEM module, and reinstalled the new one.

One way or another, the procedure to remove the instrument cluster/panel is going to happen. Either they'll admit to disassembling the panel, or somehow magically by pass it. At least this will prove at some point on 6-6-16, the mechanic very likely at one time or another had to disrupt the connection to gas gauge.