"Activation Lock for iPhone, iPad, and iPod touch" is a security feature, one aspect of which is deterring re-selling of stolen devices. To learn more click here --> http://support.apple.com/HT201365
An activation lock can only be removed using information for the account that applied the lock. If you know this information follow the onscreen steps to enter the Apple ID and password used to set up the device, or enter the device passcode.
How to remove Activation Lock - https://support.apple.com/HT201441
If you are truly the first owner of this device and it was purchased from an Apple authorized retailer or Apple itself then Apple can completely erase a device if a person can provide sufficient evidence of valid ownership. Do this online here -->Activation Lock support request - https://al-support.apple.com/#/additional-support Apple says, "Proof of ownership documentation is required," but does not state what constitutes proof. Prior to this new online service Apple typically required the original receipt issued by an Apple Authorized dealer and documented provenance (so typically it would be the original owner who does this, or a descendant with legal proof of ownership).
Alternatively an Apple Store used to provide this service but I do not know if they still do.
Nobody could have put a different ID on the device without having actual physical access to the device. If you bought the device from a non-Apple authorized retailer then the device was probably not new but used or possibly even stolen. In that case Apple will not reset it for you.
