Stopping subscription without waiting for it to expire

I recently moved to the US from the U.K. so in order to “Change Region/Country” on my iPhone I had to cancel all of my subscriptions, which I did.

The frustrating thing is that one of my subscriptions still has almost a month left to run, because I had paid for a month ahead just before I had cancelled the subscription. This means I have to wait a month before being able to change region so I can use the US App Store etc.

How do I end or stop the subscription now without having to wait a month for it to expire?