Help on how to use subway guft card

I recently bought a subway gift card from amazon sold by pinelabs which was sent to me by mail. It was mentioned to show it at the store to redeem it. I tried to use it at my nearest subway but they said they don't accept it. I tried using it at a subway store in a mall, They entered the code but it didnot work. Did anyone use this before and know how to use it ?