haw i unlock my dev i have an invoice ?????????

You have encountered Activation Lock on a second hand iPhone. Contact the person who sold you the phone and ask them to clear the activation lock. If they refuse or cannot do so then return it and get your money back. If you have the original receipt from Apple, or from an Authorized Apple Reseller for that phone you can contact AppleCare or an Apple Store (make a Genius Bar appointment first) they will clear the activation lock. If your receipt is from a non-authorized shop or individual it will not work.

What device? How is it locked, locked to a cell provider, Activation Lock, passcode locked?

What invoice, did you buy it new and from where?