I've used these in several place with different routers (including Netgear) - never had a problem. You could try changing the socket used at the back of the router, but my bet is that, despite what the shop says, that the one you're plugging into the router is faulty. Do you know anyone local where you could prove this by plugging the homeplug into a different router?
p.s. If your user name is also your email, be prepared for loads of spam. I'd change your name sharpish!