Name transfer not done by the Purchaser of my bike that was sold about 3 months back

I sold my bike on the 13th March 2021 to a person who bid via online portal. Since the person claimed to be working in Germany, he had asked one of his family member to collect the bike after transferring the money. I have the ID proofs (DL of the purchaser and the Aadhar Card copy of his family member) who collected the bike after signing the Delivery note. It was informed by the purchaser that since he is out of country, the bike will be name transferred in his family members name who picked up the bike. Now it’s been more than a couple of months and the name transfer is yet to be done. Tried reaching the purchaser but he isn’t responding. The family member who picked the bike says he doesn’t have any confirmation from the purchaser to get the bike transferred in his name (though he had earlier confirmed in doing so before picking up the bike). Pls suggest me as to what steps should I take now as I have the Delivery note duly signed by them as well as their Aadhar card copy self attested by the Purchasers person who collected the bike. Thanks much and all your valuable suggestions are highly appreciated .....