He said that the car is a surety for his money at the beginning and forced me to sign on the notary. Now he is blackmailing and saying that he will file case as I sold the car to him and not giving the NOC. Can I approach bank officials? Can he file a case by depending on Notary that I have signed? Is it valid document? I don't know his address. Now he is not answering my phone calls.
You should allow him to file a case as per the papers in his hand, let us see on what grounds is he going to file the case.
You approach the bank and get the HP details and confirm the sale.
The notarised document is to be seen for making any comment on it. If it is a loan agreement, then you can challenge it in the court about its legal validity.
even if you dont know his address, with his phone number, you can obtain his address through the service provider, you may lodge a criminal complaint with the police who will be able to trace his address on the basis of his telephone number.