Sold k-car but title still not changed over by the new owner

I sold my old k-car over 3 weeks ago and I called the 軽自動車検査協会 already and confirmed that he has not done the ownership change.

Is there a way to remove myself from the car ownership without involving the new owner? I couldn't find any information on the 軽自動車検査協会 website.

I sold the car super cheap and quickly, I didn't bother asking for his phone number or name, I just handed car over and took the cash. I can only message him on the secondhand goods website I used but he is not checking messages.

So if he doesn't change the ownership, I will have to continue to pay for car taxes and possibly get into trouble if he has an accident or something.