Holden Astra 2007: Problems with gear changes

Last December I purchased a 2007 Holden Astra CDTi automatic from a Holden dealer with 97,000 km on the clock. It had the balance of new car warranty and additional 3-year 175,000 km warranty. After a week and less than 1,000 km a problem occurred where a gear change was missed under acceleration, the engine revved wildly and on release of the accelerator, the car loudly clunked back into gear with violent force. The dealer checked it and diagnosed that a software upgrade was required and done, but the identical problem has occurred another 10 times over 20,000 km. The dealer has had the car back another three times, but diagnostics show no faults. I have written asking them to replace or completely overhaul the transmission under warranty at the next service. No reply yet. Has anyone else had similar problems?