Battlefield Bad Company 2 serial key

I received BF Bad Company 2 some time earlier this year for free from origin for some event that was going on. It gave me a choice of a few games so I picked battlefield. I dont remember if I ever tried to play online but I today I wanted to play it and redownloaded it with my Origin app on my PC. After it was done, I started it up and tried to enter the multiplayer mode which asked me to sign in. I did. The it asked for the serial key which I had no idea what that was or where it was so I looked it up and all the forums, even the help ?s in origin's customer service center led me astray. It said to find recent order history and the product and the key would be right next to it. I only found the order number which I thought was it but gave me an invalid message ingame. Then I saw it had to be a key with letters and numbers and way longer than the number i found. So I dont see the serial key anywhere. If anyone knows what I need to do to fix this problem please help. Thank you.