How can I return a physical iTunes gift card ?

Hello. I bought an iTunes gift card last Friday in a 7/11 store, but now I want to return it. It has $ 500 inside of it and I really want to return it. I just wonder how can I return it. I tried to call the 7/11 store but there's no one reply. Can I return it online? Like redeem then get my money back to my bank card? I dont know about the process at all.