Travelling on British Passport on cruise ship ex. Australia docking at various ports

including Shanghia as the second last port (Hong Kong) the last destination before flying back to Australia (from HK) The cruise company, P & O advise me in that I require a visa for the China stop whether or not I disembark the cruise vessel Shangai (stopover 18 hrs max) before boarding again to continue to HK. I believed I could apply for 72 hour free transit, now discontinued I believe & replaced by 144 hour free transit. Am I correct or have I misunderstood the visa requirements? Cannot contact Consulate to verify (no phone/email reply)