If you bought your Premium membership through Google Play, you can cancel it from your Google Pay account page, following this link: https://pay.google.com/gp/w/u/0/home/subscriptionsandservices
If you bought your Premium membership through the Apple AppStore you can cancel it from your iPhone settings. If you don't know how to do it, follow the instructions in this Apple manual: https://support.apple.com/en-us/HT202039
If you purchased your membership by credit card, and in the event that it is a recurring payment, you can cancel its renewal from the "My membership" menu.
If you can't find a way to do it, you can always contact us from the help/contact menu or by email to [email protected] and we'll help you.