Payments without consent

You would have to contact support and speak to billing.
support.xbox.com/contact-us

More to the point, are you safe from your mum. As long as she consents to you using her credit card, then everything is good. Her card details are safe and once a purchase has been made, you can remove the payment method from the account. Which is a good
idea, so you don't get in trouble of your mum for purchasing items without her consent.

First, go to https://commerce.microsoft.com and check where the debt of 6.99 comes from.

If this is a legitimate payment (e.g. you have a valid Gold membership subscription that was withdrawn while your credit card or bank account had insufficient funds), you can

pay the due amount with these instructions.

In case the payment was made without your consent (e.g. kids using your account and buying ingame items without your consent), you need to contact the official support at
https://support.xbox.com/contact-us

A friend was recently recorded in a xbox live party without his knowledge or consent, is this legal?

It depends on what state the recording was taken from. Some states have a one party consent law when it comes to recording people without their knowledge. For instance where i live it would be perfectly legal to do the above without their consent.

I would ask to speak to the manager and inform them that your child was able to purchase this from their store without your permission and you want it returned. Although it is ok for kids to buy consoles since they don't have an ESRB or PEGI rating like
games and movies, I would still tell them at the store that your kiddo bought it without permission.