How has your friend been operating the system. I have had customers with heat pumps operate them improperly. A heat pump is not meant to recover very fast it is meant to maintain, so if they kept setting it back to 60 then trying to quickly heat to 70 the thermostat was probably partially set right and it should have been explained better from the company but there is no way this should have gone on for two years without a remedy.
I think no matter what the company has some fault here but how much? How was it improperly hooked up. How does a customer not notice a heat pump not coming on and just the electric heat?