Refund for cancelled subscription

I have cancelled a subscription to the app magic piano by smule 3 times this month, it’s a weekly charge of 7.99, the past 2 weeks it has worked and I wasn’t charged but I had to yet again go to my subscriptions and cancel it and this week I was charged for it. I’m getting extremely irritated and I don’t understand why if I’m cancelling the subscription it’s still trying to charge me every week. I have even deleted the app and it’s still charging me. I don’t want the app, I don’t want to pay for it and I want a refund for this week because I have tried to cancel it every week this month.