You need to have an alternate login option on your JioSaavn account for your Facebook account to be unlinked. You can check this in JioSaavn App Settings > Edit Profile. If you do not have any other credential apart from your Facebook account, please enter an email ID or mobile number, and tap Save.
Once you have an alternative login option, please write to us from the JioSaavn App Settings using the 'Contact us/Chat with us' option to get your Facebook account unlinked.