Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
I am having the exact same problem and your solution by going to mysignin.microsoft.com also asks for an authenticator code. I am only able to write this to you from another microsoft account that I have. If i did not have this other account, I would not have been able to reply to this without needing to sign-in which again requires an authenticator code. Catch 22 after Catch 22 after Catch 22. My only solution that I have figured out is to go to my credit card company and cancel the subscription through stop payment. Your post is helpful, except it doesn't work because it requires a sign-in to authenticator, which I don't have. This is so incredibly frustrating. I wonder how many people have cancelled their accounts because they can't sign-in and as a result can't even get help to solve this problem. I bet it is a large number.
I eventually decided to contact Microsoft Sales to enquire about a deployment of 200 licences - really funny how they replied PERSONALLY. When I said that I wouldn't buy 200 licences unless they fixed this issue, they politely told me to0 contact support, and gave me the automated, robotic, AI driven crappy support number and website. Thumbs down to MS. We cancelled the credit card and I'm getting weekly emails saying its been declined. I wonder how long that will go on until the bots get the hint! Does AI take hints?