Digital DJ Pool payments are non-refundable under the current policy. Cancelling stops the next renewal; it does not refund the paid period already in progress.
You keep app access through the paid-through date. DJ and Artist app memberships are separate, so use the billing controls in the app that manages the charge.
MP3 files already saved to your device remain there after your app access ends. The online Library is download history and does not guarantee that a track will stay hosted or be available for another download.
Read the Digital DJ Pool Terms for the full policy.