Absconding Case - employee asking for work experience certificate - giving legal threats

Hi, One of our ex-employee worked for 4 month with us in year 2014 and left the organisation without notice, after followup he said he is not well and unable to join us and never communicated back.
Now in 2019, he messaged us to provide him work experience for 4 month he served with us because his current employer is asking for the same.
Since, It is an absconding case. what need to be done here? as he is reaching out to us after 4 years and didn't server the notice period nor resigned properly.
Also, he is giving legal threats over call.
29th March 2019 From India

Dear, If you have not initiated any legal action against him so far, please issue the experience certificate to avoid any legal consequence.
As per given information, he has worked more than 90 days with your Organisation.
Thanks,
30th March 2019 From India, Delhi

What if he serverd less than 90 days?
1st April 2019 From India