ipad unauthorized users

As correctly stated above, there are no other users on an iPad.

Some related reading for improvements to your security for what can be unfortunately-too-common cases for some of us:

Checklist: If you want to stop sharing with someone whom you previously shared with - Apple Support

Checklist: If you want to make sure no one else can see your location -,Apple Support

Checklist: If you want to see if anyone else has access to your device or accounts - Apple Support. 

For more detailed information:

Device and Data Access when Personal Safety is At Risk. 

And for more about how we’re getting hacked and scammed—we ourselves are getting hacked, and rather less commonly our devices are getting hacked—see these:

Scam Pop-ups, Scam Viruses, Scam Receipts… - Apple Community

Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support

Handing over our Apple ID credentials (to scammers, stalkers, crooks, etc) isn’t really about our devices getting hacked, it’s about us getting hacked. And that happens rather more easily than any if us might prefer.

An iPad is a single-user device. The only people who can use it are those who have the passcode to it. Have you been giving the passcode out to people?