PC World refuse to repair hardware fault, because of Linux

a crack has developed near the left hinge, this develops because the joint inside is failing and spreading to the casing. Laptop is only 4 or 5 months old and otherwise in good condition. It was agreed that infact there is indeed an issue with the hinge and that it will spread much further untill the display can no longer stay attached to the rest of the unit. Then I was told because I have Linux installed, I am not covered by my warranty.