Dansker her også
The problem you have, i faced that when my old phone got stolen. So less then a week ago my old phone got stolen (got it back, but bought a nexus 5 now :3) i called the insurance company and police to report it stolen, and i got it IMEI locked with the help of the police. And when that happends you wont be able to call or text from it, but your data will work for tracking it.
So my guess is that its a stolen phone and the original owner reported it stolen to the police, and now its IMEI locked.
Try and call the police and give them the IMEI number, and tell them what you told us and ask if its locked.
Great day to you!