You clearly have a previously owned device that was not correctly prepared prior to your acquisition of the device. This process, to correctly erase and remove the Activation Lock wasn’t followed:
https://support.apple.com/en-gb/HT201351
Here is some information from Apple concerning Activation Lock - and how to disable it:
https://support.apple.com/en-us/HT201365
https://support.apple.com/en-us/HT201441
Long story short - for you to be able to be able to reuse the device that is Activation Locked, if the AppleID to which the lock relates is not in your control, you must secure the cooperation of the owner of the AppleID account to which the device is associated. If you’re unable to do so, the lock can neither be disabled or bypassed. Unless you have the original purchase invoice, showing the device serial number, Apple will not assist.
If this is the situation in which you find yourself, nobody here can help you; you’ll not be able to reactivate or use the device. As such, responsible recycling is the only future for your iPad.
Sorry, this is clearly not what you were hoping to learn. Whist obviously disappointing, I hope this information is of some help - if only in providing clear explanation as to your situation.