I don't agree with giving notice without giving K's boss a chance to prove they can right this thing, and that can be done at no cost to the OP and potentially has a huge upside.
The cost to OP is all the opportunities they don't take in the mean time and whatever mental cost they're paying by persisting in a horrible environment.
It might be worth it if they had an awesome relationship with their boss, a lot of trust built up, but it doesn't sound like that's the case. If they'd a decent relationship, and decent managers, the situation would never have reached this point in the first place. Add to that the fact that the company went back on their word...
They're either liars or stunningly incompetent. Neither's worth counting with.
