You are able to proceed to an account deletion Soundiiz and removed all saved datas on Soundiiz servers at any time directly in your user settings as long you don't have an active Premium subscription.
If you have an error here, you probably didn't filled the right password or you still have an active Premium subscription (in that case, the subscription will be set to canceled anyway).
Premium users: if you have an active Premium subscription, you must first set to canceled your subscription and wait the end of current Premium period. Once over, you will be able to delete your account directly in your user settings.
If you have created a Soundiiz account with Facebook/Twitter/Google, you will have to use a Soundiiz password to confirm the delete process. You can generate a Soundiiz password on this page.
Be aware that deletion will remove your Soundiiz account and datas but you will have to revoke each access you have granted to a music service to Soundiiz directly in the music service interface.