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

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

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.