Issue
You've changed your mind on upgrading or downgrading your Heroku Postgres plan and now want to cancel the pending plan maintenance to stay on the original plan.
Resolution
You can cancel the pending maintenance associated to the plan change via the CLI by running heroku addons:upgrade or heroku addons:downgrade and specifying the original add-on.
To do so, run:
heroku addons:upgrade <postgresql-addon-name> <original-plan>
For example:
heroku addons:upgrade postgresql-colorful-12345 standard-0 -a example-app