For the purpose of ascertaining the matters and things specified in Section 1351, the commission may cause a hearing to be held at such time and place as it may designate. Before any hearing is had, the commission shall give the public utility affected thereby at least 30 days’ written notice, specifying the time and place of the hearing, and such notice shall be sufficient to authorize the commission to inquire into the matters designated in Sections 1351 to 1354, inclusive, but this provision shall not prevent the commission from making any preliminary examination or investigation into those matters. All public utilities affected shall be entitled to be heard and may introduce evidence at such hearing. The evidence introduced at such hearing shall be reduced to writing and certified under the seal of the commission.