Bomberman, just as a question, how old are you? You seem to be behaving like a particularly petulant child.
You bid and won an item that was marked “Collection Only”. The seller indicated to another that they *might* be prepared to post, and gave an indication of price, and to someone other than you. To my mind, nothing in that is binding – the binding side is in the listing terms, which is the Collection only. Now you come along playing silly buggers, demanding that this guy contact you, on your timeframe.
He’s probably sitting at home, (if he’s even read the email, I know sometimes it takes me a few days to read mine, yet alone reply) thinking “what the fuckety has this muppet bid on this for if he can’t collect?”. Now he’s thinking he’s got to go through the hassle of relisting etc just because you want to vary the terms of the auction.
IMO you should be collecting the amp, or at the very least offering the £20 postage cost, which would then be his discretion whether to accept. If it was me selling it, I’d happily tell you to piss off and suggest that you actually broke your side of the sale contract. I’d also be rightly pissed off if you then tried to neg me for it, and would throw that straight back through the ebay complaints system.