I agree with Whitey, but be prepared to be told to pound sand. The whole reason I learned how to wrench on cars is because I got tired of paying mechanics (both independent and dealership) to throw parts at problems without ever actually finding the problem. None of them ever even gave me $50 back.
On the one hand I understand mechanics not guaranteeing repairs - it is possible to replace one bad part, and then to have another bad part show up that couldn’t be diagnosed before because the first bad part prevented the second one from being able to work.
On the other, I find it tantamount to criminal the way some mechanics just throw random parts at a problem and want you to pay the bill for their lack of diagnostic skills.
Without seeing the shop manual for your Flex, I can’t tell whether they followed proper diagnostic procedure here, but it seems odd to me that there wouldn’t be some sort of basic “Will the seat heater turn on if I hook this test module up to it” test that would isolate the control module as the bad part, and would at the same time tell you if the heater works.