My iPad won’t unlock

If the iPad is on the activation lock screen you are sure that's the correct id, the iPad shows in the Find iPhone section of that account on http://www.icloud.com ?

If you were the original purchaser of the iPad (i.e. it wasn’t bought used), you could try going to an Apple Store (make a Genius Bar appointment if you do) or try contacting iTunes Support online (https://www.apple.com/emea/support/itunes/contact.html) and see if they can remove the iPad from the account - they are likely to want to see proof of ownership before they might help e.g. original receipt with the serial number on it