Unreasonable or violative existing rates and services.

If the commission, after reasonable notice and hearing, on its own motion or written complaint by any person who has a substantial interest, finds that any rate or service filed with the commission, including any rate filed pursuant to s. 368.105(3), whether or not being demanded, observed, charged, or collected by any natural gas transmission company for any service is unjust, unreasonable, or unduly discriminatory or preferential, or in any way in violation of any provision of law, the commission shall determine the just and reasonable rates, including maximum or minimum rates and services, to be thereafter observed and in force, and shall fix the same by order to be served on the natural gas transmission company. Those rates and services shall constitute the legal rates and services of the natural gas transmission company until changed as provided by ss. 368.101-368.112.