The employer withdrew the job offer 2 days before I'd start the job. Should i reply to their email? Or just ignore it? What should I do?

I was hired last month and i told them i could start asap and they told me that I'll start last month and then they moved to first week of July. I already signed a job offer and did some prework responsibilities which was a lot!! And then they emailed me last minute that they're no longer hiring for this position!! I already resigned to my old job and i couldn't go back anymore cause they already hired someone. I am pissed off. What should i do?

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