GIFT CARD

I got a gift card from my friend and i used only R40.00 from it left with R240.00 the day i was using it i had another gift card or R 1000 then i bought with it and top up with the one for R300 using only R 40 and when i left i was not given back the cards back and realised when im home and now i have a gift card no which is on a slip but they refuse me to use it saying they need a card what is it that i must do in order for me to be entitled to the remaining balance on the card I have a gift card no on a slip and I m troubled by the fact that my gift card got lost in your store and now i should suffer and now at the store they say what is i picked up the slip and how will i know how much is on the card. Hope my matter will get your attention as im really tired of fighting for what is mine.