On iOS, the subscription is managed by Apple. You can view subscriptions following the steps below:

  1. Open the Settings app.
  2. Tap your name. 
  3. Tap Subscriptions. (If you don't see "Subscriptions," tap "iTunes & App Store" instead. Then tap your Apple ID, tap View Apple ID, sign in, scroll down to Subscriptions, and tap Subscriptions.)
  4. Tap the 2ndLine - subscription that you want to manage.
  5. It will display all information about available subscription plans and active subscription plans (if any) for 2ndLine.

Alternatively, tap here to learn more.

In case you opened this accidentally but want to know a similar answer for Android, here is the article.