You need to login to your account and redeem the 15 points for the $15 credit. Go to Rewards tab>Browse Catalogue and look for the $15 credit because there are others rewards you can redeem.
please Payment history page on My Account: https://myaccount.publicmobile.ca/en/account/my-payment/manage-subscription to confirm first. Check around Dec or Jan and see if PM successfully applied the credit to your account and check the renewal transaction and see how PM used the credit. If possible, please post us the screenshot so we can help further
