Hi Trchamberlin,
The support article Connect Apple subscriptions from your wireless carrier to your Apple ID outlines the prescribed options for linking a carrier benefit subscription for use. Note that in the section "How to connect an Apple subscription to your Apple ID" a text message from your carrier is the prescribed method and the following section "If you don't receive a text from your wireless carrier" ends with this instruction:
5. "If you still can't find a button or link to connect your subscription, contact your wireless carrier."
Working with your cellular provider would be necessary if that article isn't able to help you activate the service.
Regards.