Employer not giving experience letter

My wife was working for a travel domain company in Gurgaon for their IT-related work. The company had less than 10 employees and the company owner who was also handling the COO position and responsible for all the salary and HR-related thing. As it was the travel company it was facing challenges in COVID and its owner also got infected and hospitalize. After coming out of hospital he dropped an email and asked my wife to find a better opportunity as he was not able to continue IT department. My wife understands the situation and resigned without any question or demand. She has got the new opportunity and new organization needed experience letter. My wife is trying to follow with him but he is not responding on either call or email. He is speaking with other people but not attending her calls. My wife badly does not want to lose this new opportunity and she is also not able to understand why he is doing like that I and my wife are both feeling very tensed. We are currently in Pune as my wife was working from home for the last 2 years. For since last one week we are very tensed and don't know what to do.