I had a free EGM subscription that came from NOWHERE for a while. My parents didn't know why we were getting it, and I didn't know, but it was coming to my name and we weren't being charged for it so whatever. It wasn't from Gamestop or anything. After a year it ran out and I didn't renew it.
One of your friends might've got you a gift subscription? That's about all I can think.
I've never subscribed to a magazine but I've been meaning to subscribe to Hyper (Aussie gaming magazine) for an ice age since it's really cheap and a good read. Just...keep forgetting.