@Andrew Tsybulia Similar issue I handled it, couple of days back, where you need to contact our support via one of the contacts mentioned here (you can pick Ukraine based contact) https://support.microsoft.com/en-us/topic/global-customer-service-phone-numbers-c0389ade-5640-e588-8b0e-28de8afeb3f2
This issue with phone number validation during Azure Subscription Sign up can be resolved by creating a support ticket and working with our Azure subscription team.
Create a support ticket and do share it for reference, so that I can track it internally, get this sorted for you.
Let me know if you have any further questions, feel free to post back.