Employer confirmed for Offer letter and told me to resign but later did not provided me Offer letter

Hi, I got selected in Capgemini Pune for Software testing profile. After 3 days HR called me up and asked me to submit all the required documents sent on the mail. Then again she called me up after 2 -3 hrs and started asking me about expected salary. I told her my expected salary amount. She said : 'Fine". But can you confirm from your side that you are going to join our company after your notice period?. I said "yes", definitely. If I get an Offer letter from your company, I will definitely join. So on the same sentence she replied that :"You are getting an Offer letter by this weekend only, and that is why I am talking to you and calling you and doing salary negotiation, so please upload all the documents as soon as possible and will check for your expected CTC and you will get it for sure." After hearing such sentence I repeatedly asked her and confirmed her on the same phone call that , are you sure that I am getting an Offer letter this weekend. Because ,If this is the case I have to drop a resignation mail to my HR in order to line up the things. She replied : " Yes, You are getting an Offer letter". After that again she called me up on the same day for salary negotiation by saying that they don't want to lose my candidature and want to negotiate previously discussed salary. (This was the 2nd time she was negotiating the salary) I also agreed for the final x CTC amount proposed from their side. And again on the same call I asked the same question that, Should I drop a resignation mail to my company?". She said : "Yes" Then I went to my company , and told to my TL that I have to resign. Before sending a resignation mail to my current HR , I again asked capgemini HR on the mail that : "Should I drop a resignation mail to my HR" and taken her written confirmation for an Offer letter. She also replied on same mail that : "Yes you Can" . After getting such strong confirmation on each and every call and mail , finally I dropped a resignation mail to my HR. In my current company they were about to give me a new responsibility to showcase my potential but I refused that opportunity for the sake of Capgemini and because of their HR's confirmation. My TL, HR and PM was not happy with my decision they tried to change my decision and wanted to a serve my notice period (3 months) which is quite large notice period. In that my current company was also trying to put me in trouble and was not ready to release me early. But I somehow convinced them. Now they are taking an interviews for the replacement of my position. In fact 1 candidate is hired and joined my company too. Now its beem 12 days ,I taken up the follow up for Offer letter then all of sudden a new HR comes into a picture and told me that "They have kept the client decision on hold for 20 days, they will let me know if they get any updates ". Now I sent multiple mail to both of the HRs but no one replying to my mail. Also I cannot withdraw my resignation now. What should I do now?