Someone stole my iphone and now all their stuff is on my phone?

So I lost my phone the other night so the next day I deactivated it. Someone turned it in and when I got it back all there stuff was on it. I go to try and rest the phone but it says I have to have there password to rest it. So I don't know what to do.

They won't be able to get your icloud password off it, unless you had iOS 6.

It really depends on the generation of your iphone, if it's gen 4s+ then you will need to do a factory restore on itunes, first you need to turn off "find My iphone" under settings and turn off icloud on your device to disable activation lock, then you need to plug your iphone into your computer via USB cable and open up itunes Select your phone is click "restore"

Whatever make your phone is, Go to the shop or online store ( shop is best ) , They can change the password for you

Omg! I think you should tell the police, since they stole it and its not there property to do such thing

Here's the problem. You had the phone with iOS6 on it. They put iOS7 on it before you got it back. What you are seeing is a new feature called iCloud activation lock. It's an anti-theft switch that basically locks it. Unless that person remote unlocks, there's virtually no way ever to use it again. You'll have to try the cops to make them do it. Apple doesn't do third party disputes and doesn't care. You're carrier can't fix that either. Bottom line, they have to do this or it'll never happen. Best luck.