The advice you have received is correct.
I don't know why they can't do it, but Ebay are unable to change the country on an account.
You will need to open a new account in order to sell again.
You can't use an email account that is linked to an account already, but it's easy enough to open an 'Ebay only' email account - I have a gmail account which I opened just for Ebay use.
"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)