Microsoft 365 features that help users manage their subscriptions, account settings, and billing information.
The resolution is mentioned on page 2 of this question.
Contact MS Support. Battle the dragon, keep asking to be transferred until you find someone you can convince to issue you with a new product key. They will cancel your current subscription and you start over.
It's not pretty, but that is all they have for you right now. It is a defect / bad decision in the design of the 365 admin pages. I hope they get around to fixing it some time soon!
There is easier way than calling and fighting with Microsoft Tech support and trying to get refund. As selected language is in the installation file download file URL with the parameter of e.g. "language=en-US"