Resignation accepted no relieving letter - new employer asking for a relieving letter from past employers

I have resigned from the company on 3rd Jan 2020, manager approved my resignation stating "relieved with immediate effect lwd 3rd jan 2020 no need to serve notice period" on 10th Jan 2020 since 9 months follow up with the company no response.
Please help how to handle this situation as my new employer asking for a relieving letter from past employers mandatory.

Dear Colleague,
Yes, Relieving & Exp.Letter are mandatory doc to submit when you join any new org.
Since it's been 7 months, you haven't received your separations letters, i would suggest to drop email to concern HR dept. keeping your manager in CC.
If aforesaid is already done and no response , then you should visit office once to understand the rationale or you may also loop higher authorities.
Also, if they have released you on the same date as of your resignation, you are entitled to get Salary inlieu of notice period as per the clause mentioned in your appointment letter.(do check)
<Provided, you have not requested early release and you were ready to serve entire notice period>
Regards
Piyush

Why don't you meet & ask the pre.Manager himself who relieved you for the Relieving & experience letters (or both combined in one letter). What's blocking you to meet him? If he refuses then you can ask in writing. Don't delay further.