Replacement motherboard

My motherboard failed on a brand new Latitude after 3 months and Dell replaced it with a refurbished motherboard, not a new one. I've had refurbished Dell motherboards fail on me before and think Dell should install a new one as the laptop was only 3 months old. I'm being passed around in circles between customer services and technical support and nobody seems able to make a decision. Does anyone have any idea how I resolve this without having to issue a legal claim? I'm in the UK.