To cancel a Microsoft 365 subscription of any type, you must do so from the product's Administrative Management. Make sure that there are no active users using that subscription, otherwise you will not be able to unsubscribe.
The different Microsoft 365 plans have the same periodicity and are renewed by default according to the periodicity you have chosen, which you can change from your Client Area.
If you have deleted a user, you can reactivate the user manually as long as no more than 30 days have passed. You will have to request this in the contact section of your Client Area.