Need Advice: GPU RMA issues with Memory Express

Hey guys,

I have a Asus R9 290 DCII OC that I purchased an in-store replacement warranty for 80 bucks when I got it. Over last few months was having issues with my video card. Getting weird black screens periodically. Then one day found the computer with a black screen. Rebooting didn't help. Wiped drivers, reinstalled drivers, tried different bio, NOTHING. I plugged a r9 270x in, poof, no problem. 2nd 270x, again, no problem. Wiped drivers, reinstalled, put 290 back in, same problem.

So, I sent the card back to MemoryExpress and they are saying that they can't "replicate the issues" that I was reporting. I don't know what to say to them. Basically they can say whatever they want even if the card is actually defective, my word against theirs. They can say it's another component in my system (even though tried on two different systems with different PSU's etc.).

Any suggestions on going forward?