Optum Global Solutions (INDIA) Private Limited - Loss of Employment

I was working at TCS. I interviewed at Optum for an open SWE position, selection was confirmed on Feb. ** **** during HR discussion. The following day, got an email confirmation for the same along with CTC details and was asked to complete resignation formalities by end of March (possible DOJ) and one specific instruction that “Offer letter will be released a few days prior to DOJ”.
I resigned and waited for the offer letter. On March **th, every other candidates joined the company (got offer letter * days before). I contacted about mine, after * weeks got a reply that they have limited alignments and asked if I am ready for relocation, replied positively. Again no progress for * months after Feb **, finally got a background check (BGC) form to fill, was assured of joining on June *th via call. Given date passed and no progress, on June **th got the last reply from them as “We are expediting it (the Offer letter) on priority”.
After that complete silence and ignorance, no reply to mails or messages nor picking up my calls. Fast forward to current situation, almost * months passed from the offered date, no progress, complete ghosting. No reason provided for not releasing the offer letter for the job. I resigned only based on this offer and now I am unemployed.
I suffered mentally and financially (my family too) because of the loss of employment, I had a decent paying and very stable job, and this whole treatment by Optum has left me devastated.
I think as there’s no contract or offer letter, there are only limited options I can pursue. My case is if they were unable to continue at any point with the offer, they should’ve clearly informed me well before instead of saying that they are working on it, and giving false joining dates. I would’ve gone back to my previous job.
Their deliberate action has costed me my job along with immense mental and financial hardship. All they had to do was write an email saying “Sorry. We can’t continue” and it would have all fine.