A free trial for a great service you really need is brilliant. Until you forget to cancel before the deadline and the subscriptions kick in. Does this sound familiar? Amazon prime, Disney, cable sports channels etc etc. These services keep charging until you TELL them to stop. Its easy...On your phone go to Google Play - Menu- Subscriptions - Manage - Cancel. DONE.
iOs (little harder) Settings - Apple ID - iTunes & App Store - Apple ID (again) - View the ID to get to the a/c info and scroll to subscriptions. Little more complicated but worth the $avings. 
ITSS can help with any tech queries Mon-Fri 8-4.