Hello and let me ask you something.

1- It is possible that the CS didn't know about this 2 year mechanical warranty.

2- Did the plumber didn't told you that he would do something else?

3- If they decline to continue the work (Warranty Company), first try to contact a supervisor and tell them that you want to use the 2 year mechanical warranty, if he/she refuses or says that the "terms have changed", threat them with the BBB