There's not much you can do if the seller doesn't reply. He will probably open an unpaid item dispute in order to get his fees refunded, which will lead to a strike on your account. This kind of thing wrecks the sellers auction and cost him money. His fees for a £300 item will be £30.
It's a clever 2 year old that can not only remember your password, but type it in too. You are entirely responsible for your account, no matter who bids.
