Your Apple One subscription starts with a free one month trial, but only for the services than you haven’t had a trial for before. Previous Apple TV+ subscribers will find that the trial doesn’t include Apple TV+ for that first month. For a seamless transition, you would have wanted a one month overlap.
Either wait it out, or re-subscribe for 1 month, and then Apple will automatically cancel Apple TV+ again when the paying billing cycles start for Apple One.
Apple One - Apple
* The Apple One free trial includes only services that you are not currently using through a free trial or a subscription. Plan automatically renews after trial until cancelled. Restrictions and other terms apply.