Hi. My name is*****'m a camera repair technician with over 20 years in the business and I'll be glad to help you with your question today.
With the card out and the door open, use a flashlight to look into the card slot and see if any of the pins at the bottom are bent.
Normally, when this happens, it's due to pin damage. If that's not the case, the camera will need to be looked at by a technician to troubleshoot and identify the problem. Unfortunately, I can't recommend any shops in Australia but you might want to check locally for a repair shop before sending to Canon for repair. If you do decide to send it to Canon, check first to make sure they still work on these.
Just a note to see if I can be of any further assistance?