Dear Arathy,
What has happened to you is shocking. If you were not issued an appointment letter, and the PF UAN number was not disclosed, it was as good as casual employment. Nevertheless, your educational certificates have been kept in custody.
At this stage, getting back your educational certificates is important. Send a letter to your employer requesting the return of the certificates. Send this letter by Speed Post only and not by email. However, after sending the hard copy, scan the copies, including the receipt of the Speed Post, and send these by email. If he does not oblige, then file a complaint with the labor office.
In the same letter, you may write about furnishing details of your UAN. If he does not oblige, then you may file a complaint in the PF office.
Average persons become uneasy when required to approach government offices. However, don't develop cold feet. They will be friendly. However, they could be busy and expect you to talk to the point. Preferably, speak in the local language.
Thanks,
Dinesh Divekar