When you buy a overlord card , of witch there is a duplicate , do you get both cards or only a single one of them. The rules state that you can buy a card with your exp points , so i would assume that you can only buy 1 card at a time and would have to pay again for a duplicate card if it is. Please correct me if i am wrong.

You are correct. You get only one copy of the card.

Thank you very much.

Thank you very much.

It should be noted (just in case it's not clear) that you can spend more XP and get the second copy of the card as well- there is no rule against buying both copies (that's why there are more than 1) and they'll count as separate cards in the class as well. That is, you need to have bought 2 Warlord cards in order to buy a level 2 Warlord card. You could buy "Blood Rage" twice, and then buy "Expert Blow" later (since each "Blood Rage" counts as its own card.)