Dear Rustam.Y,
Hello! Welcome to the Microsoft Community. I'm glad to be able to assist you. If I misunderstand your question, please let me know promptly.
It looks like you can't activate your Office Professional Plus 2021 over the phone. I understand the frustration this issue is causing you.
I really wish I could handle your question, but unfortunately, questions about the "Professional Plus" editions are beyond the scope of community support. It is more appropriate to post it on Microsoft Learn (English only), where there are more advanced forums and more users posting these issues, and you can click "Ask a Question" where experts can provide more professional solutions.
Here is a link to the forum where you can come up with specific scenarios and share your ideas to help resolve the issue.
Office - Microsoft Q&A
I'm sorry to have to direct you to another forum again. Sincerely hope that your issue will be properly handled after contacting the right department. Thank you for your understanding!
Best Wishes
Pyke.D | Microsoft Community Support Specialist