iTranslate App Charged a Yearly Subscription After I Canceled

I purchased the iTranslate app, which advertised a one-week free trial. According to the terms, my credit card was supposed to be charged after the one-week trial period. I used the app for about a week, but I did not like it. Although the app claims it works offline, it did not work offline at all. Because of this, I canceled the subscription.

However, even though I canceled it, my credit card was still charged for a full one-year subscription. I do not understand why a yearly fee was taken from my card even after I canceled the service.