We have had office 365 for over a year, purchased through a reseller.
Recently the reseller made one of the email addresses on the account a global admin.
This seems to have switched on Two Factor Authentication on that account - however that had not been set up by the user so they now cannot access their account. There appears to have been a number associated with the account that nobody recognises (it ends in 99 and several of the tech support people have suggested this is a default number used by Microsoft?).
The reseller seems completely unable to resolve the issue.
Any advice on how we can get two factor switched off on the account, without being able to access the account, without the help of the reseller?