It would be up to Microsoft to say why they did it. It's probably buried somewhere in the sanction documents. [1] If Microsoft are complying with a sanction then perhaps they may have issues getting a refund, but could at least open a ticket to get an answer if they have not already. Maybe there is a corporate lawyer on here with experience in this matter?
[1] - https://ofac.treasury.gov/sanctions-programs-and-country-inf...