It is charging me every week without my permission – TOEFL TestBank: Prep & Review Review

I am really not satisfied with that . It's setting is really week. And I bought the app just for a week for 99 cent but it is charging me after that every week without asking and I can not cancel it . Because there is no way in its setting and I have sent an email to its company but they haven't answered for 3days.
Review by Farnazest on TOEFL TestBank: Prep & Review.