If it was stolen from the original owner then you don't really own the device legally and this is the anti-theft part of activation lock functioning as designed. If you're an innocent third party to the original theft, your remedy is to get a full refund.

If it was just because the original owner forgot to disable activation lock, you should be chasing them to unlock it for you. If they refuse, your remedy is to get a full refund.

edit: reputable recycling places require you to have disabled activation lock on functional devices, or they don't pay out.