Live user not found in stage and dev
Acquia works on a three-environment system. When working in such a system, code moves up, from dev -> stage -> prod, while databases move down from prod -> stage -> dev.

You should always consider content on dev and stage, such as nodes, users, taxonomies etc, as temporary. This is because the way to migrate content is by migrating the entire database from prod -> stage/dev, or sometimes from stage -> dev.

In order to get your user on all environments, you would create the user on prod, then migrate that database to stage and dev. You will then be able to log in with your user on those environments.