You can always cancel a subscription, even when it is still active. Also, when you cancel a subscription you will still be able to use your subscription during the time you’ve already paid for.
You purchase the weekly subscription on the 1st of January. You then decide that you want to cancel the subscription on the 2nd of January. In this case, you will still get all the rewards from the weekly subscription until the end of the week.
Please find the respective procedures for Google Play and iTunes via the following links:
If you are having issues with a subscription, please send us a support-request via this link.
Make sure that you add a copy of the receipt of your purchase, so we can quickly review your situation.