Are you sure it's a basenji? 20.1kg is too heavy for a basenji. Medjai is a light basenji (also a little short) and he only weighs about 8.1kg. I think standard for a male should be about 11.3kg.
He will eat if he's hungry enough, just do the best you can with picking something he'll like based on what the rest like and he'll eat it in time. If the vet says that nothing's wrong, go with it. It'd help if you could post pictures.
Yeah, that does sound HUGE….like almost double the accepted weight for a male Basenji. Must be a mix with something. Can't wait to see pictures.