I need a phone number to speak to a person someone is trying buy on my account.

If someone has stolen your account and is using the payment card information in the account to make unauthorized purchases, there isn't anything that Microsoft can do about it. Microsoft can't see who's sitting at the keyboard typing in your payment information, and it isn't Microsoft's responsibility to check whether someone entering valid card information is actually entitled to use it. Closing the account won't make any difference, since the thief has your payment information, whether your account exists or not.

This is something you have to address with your bank or card issuer.