If you have to work order you can read exactly what that 1st dealer claimed they did. It probable should say something like:

A. Customer complains that passanger heated seat element on backrest is not heating up.

Then there should be a reponse by the mechanic saying something like:

A Checked heater element and found broken wire. Replaced wire and tested heated seats and foundit is okay. That is if they did some sort of work. Or, it should state, there is no such heater element for the back rest. No further action was taken. Basically what I'm saying is the work order paper should have exactly what was done on your car. If they claim they did work it should be in writting and if the work is bogus because there was nothing to work on, then you have a lawsuit case.