Adult account as child account

Is the account in question a child's or adult's account? If its a child account you may want to change it to an adult account and give it a shot.

Adult accounts cannot be made child accounts. Only child accounts can be converted to adult accounts. Not the other way around.

Hello PhilipBasgal,

Thank you for posting on the Xbox forums. We understand that you are interested in changing a child account to an adult account. Once an account has been established as a child account, it cannot be changed to an adult account until the child turns
18. The best way to manage the child account is to
add it to a family. This requires an adult account to add the child account to the family. Once the child account has been added to the adult account's family, the child account will be able to access online features. Be sure to let us know the results!

So, if I understand, you account is an child account and you want to unlink your parent's account from yours? Unfortunately, child account are not allowed to be managed without and adult account attached, you can ask yours parent's (adult account owner)
to contact support and ask for a change of adult account, re-alocating the child account to another MSA adult

You can change a child account to an adult account, but you can't change an adult account to a child account. In order to manage them, you would have to create new child accounts for them.