Request a Refund

This website (musescore.org) has no payment/subscription service. You are likely talking about the Pro subscription of musescore.com (See What is the difference between MuseScore.org and MuseScore.com?).
They offer support for account and payment issues via support@musescore.com (8/24h 5/7d, regular business hours, Kaliningrad time). You may also use the "Request a refund" button under "Contact us" link at the bottom of the musescore.com website.

Nobody on the musescore.org forums can help you with your request.

See also How and where to ask for support