Delia

We have replaced the coolant thermostat three times now, and now we are being told thermostat housing melted to block, after repair found cylinder head gasket is excessively blown. Found coolant purges from cooling system while running due to exhaust gasses leaking into cooling system. Would this be caused due the thermostat not doing what it's supposed to be doing in the first place. And now it's going to cause thousands of dollars to fix my car.