My heart dropped when I read that you had lost your little one, Im so sorry.
I know how quickly you can get attached to these little pups and its heart breaking when they leave us.
Just remember that you gave him the best possible care, and made his last few days the best.. he was with a vet and wasnt in pain. You were a good mom to him and he will remember it.
When you feel strong enough I think you should take legal action against this disgusting 'breeder'. Your boy was far too small, 600grams at 5 months old is disgusting.
This is what happens when these greeders breed for 'tinies' or 'teacups' they are risking their health.
I hope you can get justice for your prince and that 'breeder' gets everything he deserves.
Good luck.
Also would you be able to tell us the name of the kennels or the website for future buyers so they know to avoid this scum bag.
Thank you.