Probably better to move on while you have the decision in front of you. If they can you it's a bummer starting up again. And it make them look right!
Over the past 15 to 20 years I've gone to work for some companies complaining of the same as yours with my experience being highly desired to solve the on-going customer problems only to find out that there are a lot more of "them" out there than there is of me. Intelligence is in minority. Stupidy is in majority.
Bottom line is they weren't interested in fixing their business. All they wanted was a whipping boy and I was it...so I moved on. And they were very, very mad. Course then they called me with referrals to fix the exact same stupid install and service problems BUT I got paid based on my rates and I got to do what needed to be done without any interference from the stupid manangers.
This new world we live in amazes me in how unbelievable stupid HVAC managers/owners of, mainly, large companies can be. Problem is they still make a lot of money doing things wrong so they have no incentive, none at all, to do it right.
Move on, that's my vote.
"The American Republic will endure until the day Congress discovers it can bribe the public with the public's own money.
- Alexis de Toqueville, 1835