If Listing Sync Pro is activated, the syncing process will not stop until the remainder of the billing cycle, even when the product has been canceled.
To stop the sync immediately, you will need to first cancel the product, then click the "force deactivation" button from the kebab menu.
If Listing Sync Pro is not activated, simply toggle the "Sync" switch to 'off.' Please note that since Facebook and Instagram are closely linked, toggling the Facebook switch off will also toggle it off for Instagram.