Sold a car a few months ago but the car is still in my name

I dont have a formal notice of disposal (but i do have a written reciept that is signed with all notice of disposal details).

Anyway i havent copped much other than $10 is tolls (no biggie)

But not happy the fact he hasnt transferred (though i made it a deal)

Anyway im sure the RTA will accept my reciept

But my question is, Am i legally allowed to cancel the plates?