Resetting Joplin Cloud and encryption fails

Using Joplin 2.8.8 on macos and Windows and JoplinCloud Sync

I have a JoplinCloud Basic subscription and want to start over syncing on a clean slate. I deleted all notes and note history, before reinstalling the Joplin app. Now, when I set up encryption and then enable sync the app chooses as active encryption key the oldest Masterkey, which was the encryption key for my data before starting over, but is marked as disabled now.
After creating a new encryption key and enabling sync, upon first synchronization the app switches the active mark from the new encryption key to the oldest one.
It seems not all data was deleted from JoplinCloud, as the cloud dashboard notes some 7mb used, but I cannot find an option to delete all data stored in the cloud.
I have signed out of all active app and reinstalled the app multiple times.
How can I wipe the JoplinCloud data short of deleting the account, which would mean losing the subscription I paid for?

We don't really support this kind of workflow at the moment. Why not keep the master key you have there? You can change the password if you're worried it's compromised.

Some form of full reset/wipe for Joplin Cloud would always be welcome :).