*****,3 for 2 promo

I have recently went shopping this festive season and purchased a coat from.legit and a necklace when I reached the cashier she advised why don't I take 3 items and get the cheaper free so I was taking to if I go and pick a third item will male no difference I'm getting it free so I took another chain set, I got hone tried on the coat only to realise the coat was just not my style so I went to legit chatsworth to return the garment so the cashier did a cash refund and gave me a refund value of R250 of my R300 marked coat, I had advised the cashier that its incorrect and she advised that I took a promo buy 3 and get the cheapest free so of I return a garment on the receipt they will subtract the free garment from the other garments I was in utter shock, so iv asked the lady why agent we aware of this as if I knew this I would have not taken a third item nowhere in my receipt states this neither anything in the shop states T's and c's apply , the cashier advised that they can't answer me this cos they didn't even know as they get all instructions from head office, . that means if iv purchased 3 items to the value of R100 I'll be paying R200 and due to the one free being R100 , and if I return the 2 garments I'll only recieve a R100 ! This is not fair to us consumers at all discount the products instead or explain us this sum where as I wouldn't have taken an unnecessary 3rd item and loose value of my other items! I need sum.answers! And I would gladly appreciate if u guys can explain as I still have to return my coat but Im not going to loose R50 for sumthing u guys forced on me