Why am i being charged $ 19 extra to cancel my subscription

You are never charged to cancel a subscription. But if you have already been charged for the subscription it will run to the end of its current term. You can’t cancel a subscription retroactively.

You probably missed the billing date before you cancelled and you owe for one more month.

Cancel your subscription to what? Is it an annual plan? An in-app subscription?

If you see "apple.com/bill" or an unfamiliar charge on your statement - Apple Support