activation lock

Only the original owner who set the Activation Lock can remove it. Without their Apple ID and Password, the device is useless for you. We cannot help and Apple will not. If you cannot return the device and get your money back, you are out of luck.

You can't. You have purchased a totally useless iPad. Apple will not help you. We cannot help you. Activation Lock can only be removed by the person who locked the device and since you don't know this person, there is nothing you can do, except recycle the device responsibly, or use it as a paperweight.