prestige auto repair didnt replace thermostat when replaced water pump Salem Oregon

my 2002 volco v70xc was brought to there shop to replace cam shaft seal beause oil was dumping out of it. while they did this they replace the water pump and did not replace the thermostat. not even a year about 6 months and while driving home from work it overheated and it blew a head gasket. which i brought it back to them to see if  fixable and they said it needed a new motor and cost $4000-5000 for a new motor. all this happened because the thermostat went bad and if the would of replaced it when they replaced the water pump like most mechanics would dowhen they worked on cooling system.  so this all could of been prevented if they would of done it in the first place. then wouldnt fix or offer any help fixing or replacing the motor. even the mechanic apoligized for it because he knew how much money i spent on the car the last two years($4000) and them telling me sorry.