The PF authorities might have asked for an indemnity bond following scheme 72(6)(ii) of the Employees Provident Fund Schemes. Correct me if I am wrong. According to the said provision, if an employee's account remains unclaimed for three years from the date on which the amount became due, the same will be transferred to the Unclaimed Deposit Account. When a claim comes after such transfer, the amount will be paid out of it but only after confirmation that the claimant is the member or is authorized to claim the amount as a spouse or children nominated by the member before his death.
You can mention the reason for not withdrawing the PF as "I kept the account pending for transfer to a new account when I get employed in a new establishment, but unfortunately, that did not happen, and in the due course, due to oversight, I missed to withdraw the funds." The bond/affidavit shall be made in the presence of a Notary public. In case you had an overseas assignment for these three years, you can mention that you left India but not permanently, with an idea of coming back to India and to take up employment but failed to get into.
Regards, Madhu.T.K