American Home Shield N/A AHS contractor lied about diagnosis of my tankless water heater , Internet

I have an American Home Shield Contract.  I called and reported our Tankless water heater wan not heating the water in a normal fashion.  Water heater is in a garage.  Garage is insulated and the garage doors are insulated.  When the contractor arrived (PLUNB GENIUS) we just chit chatted for a few minutes.  I asked the 2 men how much work do they do for American Home Shield.  They  said just about all their work.  Then he examined my Tankless Water Heater.  He asked me how old was this unit.  I told him almost 7  years old.  He told me the thermostats were no good and the reset buttons were not working properly.  He came down from the ladder and said the unit is shot.  I needed to replace the unit.  I asked hi what caused the problem?  He said that old age caused the problem.  I said ok.  He told me he had to call the company (American Home Shield) and discuss the matter with them.  I said ok again.  He spent about 15 minutes talking to AHS.  He then came into my home and told me that American home Shield refused to cover the Tankless Water Heater issues.  I said why.  Because they covered all parts and labor.  He told me HE TOLD AMERICAN HOME SHIELD my Tankleass Water Heater Froze.  And that is what caused the problems.  I told him "You told me old age caused the problem.  The Heater just wore out.  Why did you LIE and tell American Home Shield it froze because he knew that was not true.   He said that was his opinion and that was that.  He said he was not obligated to tell me his reasons.  I  got so damn mad at this guy simply because he lied and he knew that freeze negates the contract.  I have an infrared thermometer and I am extremely careful about temperatures in my garage.  Temperature outside is 19 and temp at water heater is 51.  Heater is mounted on an interior wall and it maintaines nearly a onstant  51 degrese.