Hi VladimirG,
Thank you for post here.
To verify a domain to Office 365, we need to add TXT/MX records at DNS hosting provider first. Regarding to your situation, I would like to suggest you contact your domain registrar to check whether they can provide you a few months trialed DNS hosting service. If yes, then you can add your custom domain to Office 365 continuously.
However, this issue is outbound of our Office 365 support scope, I would like to suggest you contact your domain registrar for more detailed information. If there are any questions when adding domain, please feel free to post a new thread in this forum, we are happy to assist you.
Thanks,
Edward Qu