If you received a bill from either Google Play Store or Apple’s App Store for Glow, your account was likely enrolled in Glow Premium subscription.
If you enroll in a free trial offer of Glow Premium, you must manually cancel your subscription at least 24 hours before the end of the trial period. Failing to do so will result in an automatic renewal of the yearly subscription.
If you attempt to enroll in a second premium trial (each Glow account is only entitled to one free trial), your account will automatically be enrolled in the yearly premium subscription, and your account will be charged accordingly.
Please note that the Google Play Store/App Store will bill you for the subscription up to 24 hours before the end of the trial period.