These are UK boards - you might get better advice asking in the forum for your country.
In the UK, as long as you can prove delivery to the address used by the buyer at checkout, you would win your case.
However, as you have discovered, it can take some time.
I don't know what you sold, but personally, I would have taken something of that value to a 'bricks and mortar' auction house.
"There are two ways to be fooled. One is to believe what isn't true; the other is to refuse to believe what is true.”
Søren Kierkegaard, Danish philosopher (1813 - 1855)