Apple ID registration

Hi! I am hoping someone can help me....

A previous employer has got in touch (I left them nearly 18 months ago) to advise my apple ID is registered to their work iPad and they cannot reset it to factory settings without an authorisation code from me.

I don’t feel happy giving them any codes and passwords and I have checked my account to see what devices my Apple ID is registered to and the only Devices I have on there are my own iPad and my iMac.

Can anyone advise? i don’t understand how my Apple ID could be registered and it not be on my list? Can I remotely remove it as I’m not happy giving my details.

Any help would be appreciated!

Thank you!