musescore selling my score | MuseScore

It seems they are selling all your (and everybody else’s) scores.
Did you read the Terms of Use?
By uploading anything, you are giving MS the license:
By posting any User Generated Content on, through or in connection with the Service, you hereby grant to MuseScore a limited license to use, modify, delete from, add to, publicly perform, publicly display, reproduce, and distribute such User Generated Content[…]
And they will not sell the user generated content ‘outside the service’:
Except as expressly provided for herein, this limited license does not grant MuseScore the right to sell or otherwise distribute your User Generated Content outside of the Service.
Nothing about they cannot sell it inside the service. Distribute does not mean for free.
The license you give is perpetual, you cannot opt-out (even if you delete your account)
.3 The license you grant to MuseScore is […] perpetual (meaning that no termination of this Agreement will affect the license granted by you)[…]