Just take it back and tell them what's up! Yeah no way you should touch the cpu for bent pins cause if they are they will blame you did it when removing the cpu.
Tell them you've been told online its either from bent cpu pins or a bad motherboard.
If they give you any grief remind them that you remember them having the same issue when they were testing the board when you requested more ram from them before so..
Be nice if they remove the cpu for you to check yourself but I bet they won't want that but request it.
If they don't have another mb to replace it tell them you want the asus rampage 10 anniversary edition! Remember your Nvidia hb bridge must match the spacing so the motherboard needs to be a 4 way sli board for your bridge to fit.
And no that mb is not so old that it can't have win10 installed.. that's there f'up. They should be putting win 10 on it.. remind them of all the issues but stay calm. Your not happy and you have a right to not be happy with your overall experience with them! If refund is an option go for it!
If you want something done right, doing it yourself is always best.