My iPad is not allowing me to sign in with my Apple ID and it seems like someone else is using my iPad to manage my settings and other connected devices via email and my contacts

Generally, if your iPad is centrally managed, it most likely doesn’t belong to you. Did you purchase this iPad - and if so, was it purchased new from Apple?

If your iPad is externally managed, by a third-party, you’ll find an installed Management Profile:

Settings > General > Profile

Successful removal of a Management Profile will generally require removal by the Administrator of the system that manages your device. This is usually a Corporate IT Department, or the IT Administrator of an Educational Establishment.

More information about Configuration Profiles:

https://support.apple.com/en-gb/HT205347

When did you buy this iPad? You need to return it for refund. It was NEVER properly prepared for a new user and unless you know the person who this iPad is tied to, you cannot use it as your own iPad.

Buying used devices which were not removed from Activation Lock properly can lock you out of the device during an update at some point, rendering the device 100% useless.

I'm not 100% positive this is your situation, but when you said you bought it used and you're having Apple ID issues, there's a strong chance this device should be returned.

I have asked the hosts to remove your personal information; it is a bad idea to post your phone number or any other personal information on a public online forum where such details can easily be copied.

And you need to be careful buying any used device from someone unknown. I suggest you return it immediately for a refund. The only place I would buy a used device is from the Apple refurbished section of the online Apple store - you know that it was prepared properly.

A picture is often said to be worth a thousand words, but despite your attached images, your actual issue is not at clear.

Please review this document - and then attempt to describe your problem:

https://discussions.apple.com/docs/DOC-5931