Had a contractor 3 years ago install new wood engineered floor over carpet underlayment. I was told that it was done all the time, and foolishly took him at his word.  
Now, the flooring isn’t level and the seams on the wide-panel flooring almost cave in with footsteps. Do I have any recourse against the contractor in terms of having them come back and do it properly (replace underlay with plywood) or is this just an expensive lesson I have to learn?  
Thanks!

Update/edit:
I can’t add a comment above, but yes when I say underlay I mean carpet padding. Believe it was 1/2” carpet padding, and currently emailing the wood floor manufacturer to confirm that it’s not per installation instructions. I’m thinking he did it to save on need plywood as he started the project during covid right when board costs skyrocketed