My 2 wheeler sold to an unknown person, but he didn't transfer ownership

Respected legal team, I have been sold my 2 wheeler in Dec/2020 to an unknown person through OLX chat. At the time of selling, i have given bike along with original RC of bike. But i have not taken any proof of written proof, etc from him. Except mobile number, i dont have anything of that person. Also even i call from any number, he is not answering and sometimes he says that wrong number. Even OLX chat is not available, as OLX does not store any chat more that 30days as per OLX T&C. Its my mistake only. My bike is registered at Koratla, Telangana. But i have sold my bike in Hyderabad, Telangana. Please help me what steps i can take legally. Even if i want to apply for new RC, the bike was in Finance. I have cleared all EMI's, but 1 EMI was check bounce 7 years ago. As i didn't feel to sell, i didn't take care of that. Now that finance people are saying, the file is under hold. This may take long time, cannot say time. So i cannot go with new RC. Please help me out any legal advice. Best idea is appreciated in advance. Thank You all.