Subscription cancellation.

Hi,

My son tapped on an instagram link for an app. I did not want to commit to any subscription. Unfortunately, after a week I got an email about a billing that had happened on my card. I tried to cancel from the apple ID subscriptions on an Iphone but I do not have an option to cancel. Kindly assist, this is a weekly charge and it's a nuisance to me.

Looking forward for a positive response.

Thanks,