Received Initial_Releiving_Letter but didn't received Service certification

Hi All,
I served in a well known MNC for 3 years and later came for higher studies in abroad country. On my relieving letter it was mentioned that I will get service certification letter in coming days. Then when I joined my university I need to submit some documents related to my work experience for job placements. They are looking for service certification, now I don't know how to proceed with it.

Please contact your ex-employer immediately

Dear Friend,
If you have following two documents;
1. Joining letter/appointment letter/Proof of joining date mentioned any where like pay slip etc.
2. Any document certifying your last working day eg. letter from employer accepting your resignation mentioning the last date to be.
Please note you have not shared the contents of the last letter given to you.
Warm Regards
Bharat Gera
HR Consultant
9322404765