How can i unlock a brand new Samsung S6 edge+ from Sprint?

[Norval Baker]

I purchased this phone outright from someone that got a upgrade but decided to stay with her iPhone. I broke the round tabs on the side to open it for the first time, actually at a Sprint store for them to unlock. They wouldn't and said I needed to call Sprint customer care, but since I'm not a customer, they wont give me the unlock code.This phone has never been activated and has a clean IMEI but nobody has ever used it. It's never been activated through anybody.I just want to unlock it so I don't have to use it with Sprint. The phone is absolutely brand new and has never been used with any carrier. Does anybody know how I could get the unlock code for this brand new phone. Thank you so much