iPad mini smart cover fault

I bought an iPad mini a few months ago with the apple smart cover to match and protect the screen. However, when holding the ipad and cover in a particular place, the cover slides up/down and across the screen, making gripping it unpredictable. My nice shiney iPad mini has since slipped out of my hand when taking it out of a bag on two occasions, landing on the floor. First time, only minor cracks on the screen, so no real problem. Second time the screen completely shattered. I'm reasonably confident I'd have been better off without the smart cover at all. At least I could hold the iPad mini properly.

I've since taken this up with the Applestore Bull Ring (Birmingham) on the basis that whilst this is not a warranty claim, the smart cover is not fit for purpose. The Supervisor is not authorised to offer a replacement iPad or cover as this is not a warranty claim, and comes under accidental damage. Instead I have to raise my case with the in store manager by email and take it from there.

Any good suggestions on how to resolve this? Am I wasting my time pursuing this further? Is this a common problem?

Thanks