If you've been double charged while purchasing a membership subscription using iTunes via an iOS device, you can learn more about this issue below.
Medium currently offers different subscription plans for the membership subscription. If have an active subscription purchased through iTunes, it is possible to change your subscription plan before the end of your billing cycle.
For example, you can change your plan from a monthly subscription to a monthly subscription with free trial. When you do this, you are replacing your current subscription with an equivalent subscription. Apple calls this process “cross-grading.”
When you do that, a new subscription is started at the same date that you perform this action, but your billing date will change.
Any prorated refunds for the original subscription will be automatically issued by Apple, and Medium is unable to apply those refunds for you.
Note: If you switch from an existing plan to a free trial plan, you are not longer eligible for the free month.