Removal of old tariffs question?

river_kwai

What happens when energy company remove an existing tariffs and introduce new tariffs? Do customers on the previous tariffs stay on the old tariffs, or are they moved to the new tariffs? Does that mean companies maintain different tariffs for different customers based on the their joining date? When company announces price rises, does it apply to all tariffs individually, say a company increases prices by 30%, does the 30% apply to each of the tariffs?