It sounds like a typical early stage startup - horrible code (often inherited from contractors), nothing solid in place, no unit test, no processes, no idea what the final product will be like, upper management never available, super small development team, constantly moving goalposts, constant requirement changes even contradicting earlier requirements, etc
I'm assuming the company is not generating revenue yet or if they are, not much at the moment?
I've been in this situation many times before and started getting used to it even excelling at functioning in such an environment - if this is your first time in such a chaotic environment, I'd suggest sticking around a little longer to see if you get used to it, if it absolutely drives you bonkers afters let's say 6 months, it's not going to get better anytime soon until they get bought out or go big.
You have the power to change things and steer things in such a way that the team becomes something that you'd want to work with, the tech becomes something that you want to work with - once those things are set (by the early pioneers like yourself), it'd be hard to change again.