Unknown account linked to my Microsoft account

I have Just linked my Microsoft account to my sons nintendo switch so he could join his friends on minecraft, but when singed in there's a linked xbox live account that has never belonged to me!

I can't find anyway to remove it, they must have hacked me years ago but with no credit card information on my account and me not having an xbox it must have gone unnoticed,

I'd like my son to have his own account and not some hackers left behind account.

Thanks

Adam

:)