Company is not ready to issue experience letter. What should I do?

I am working in one of the IT company. I am working over there since February 2013(8 years and 4 months now). Company proposed me to offer 2 years bond(Which will going to start from 1st July 2021 to 30th June 2023) in March 2021. At that time I was in the impression to accept the bond, So I wrote " I am ready to accept the offer please let me know the next steps(bond signing step)" in Skype. HR replied that "Okay we will do it soon". But after that no steps taken place related to the bond signing by HR. So there is no signed papers for the bond. Now, In June 2021, I got better opportunity from another company so I informed HR on 24th June that I am not ready to accept the bond. But after that HR said that "You can't step back after agreed for the bond". And finally I resigned on 30th June 2021. Now company is not ready to issue my experience letter and also now ignoring all my messages and emails. I am associated with the company more than 8 years. Please guide me what should I do?