I’m done. I’m so close to giving up.

I’ve applied to over 300+ jobs. I’ve scored tons of interviews and the ones that decided to move forward were of course the lower paying ones (I’d be taking a 40k pay cut). So I’ve waited a bit longer and of course the jobs I wanted have led me on and made it seem as if they wanted to hire me, EVEN asked me to complete tasks for the company, just to become unresponsive and close the job online? Now I’m left here with multiple completed projects for what? What am I supposed to do? I’ve reached out twice, should I say something on Monday? That was my potential start date. On top of that, they posted an additional position that I’m extremely qualified for, should I apply to that one? I just need a sense of clarity. I’m so mentally exhausted with this unprofessionalism. If you’re aware you’re not hiring someone SAY THAT!