Dissatisfied customer

I always wait for the 3 for 2 special at the Body Shop. Because let's face it, it can get a bit costly! I am running low on products and have been trying to checkout my items since last week. Only to get an error!!! I make my way to the store only to be told we don't have that special and I should rather buy the items online!!! Thats fair I agree. BUT HOW DO I PROCEED TO PURCHASE IF IM GETTING AN ERROR!! I'm really unhappy with this whole situation. I took time out just to go to the store and I still have no resolution!!