Your billing preview appears as shown.

Removing a user from an Atlassian Cloud Organization does not affect the subscription plan for the products. The subscription plan remains the same until you change it manually or it expires. The billing preview shows the estimated cost for the next billing cycle based on the current number of users and the subscription plan. If you remove a user, the billing preview will reflect the reduced cost, but the subscription plan will not change12

References = Manage product access, Manage your bill for Standard and Premium plans