mechanics lien waiver

Roofer does the work after a hail storm.  Home insurance company issues payment to the home owner and the lender on the property.  Lender will not sign the check without a lien waiver, so roofer signs the waiver.  Lender signs the check and the home owner keeps all the money.  When the roofer asks for it, owner says, "look, you said paid in full."  We will get the money for the  roofer, if it is not already gone.  I have lots of ideas how the roofer should have better protected itself.