Try this steps on your computer and check this link:
iTunes Store: Purchasing and managing auto-renewing subscriptions
http://support.apple.com/kb/HT4098
1. Launch iTunes on your computer.
2. Choose Store > Sign In from the iTunes menu.
3. Enter your Apple ID and password when prompted.
4. Choose Store > View My Account. You m ay be asked to re-enter your Apple ID
password. Click View Account .
5. From the Account Information screen, scroll to the bottom of the page to the Settings
section.
6. Click Manage to the right of Subscriptions.
7. From the Manage Subscription screen click on the subscription that you would like to manage.
8. On the Edit Subscription screen, you will see the current subscription status and
subscription details.
9. Click the Off radio button to turn off Auto-Renewal.
10. You will see a confirmation window asking you to confirm.
11. Click Continue to proceed.