Hi Sharon - did your parents die in South Africa? If so their deceased estate files may be on NAAIRS
www.national.archives.gov.za The information on the Death Notice, which forms part of an estate file may be helpful. Naturally if adoption comes into the story this would not be the avenue to pursue. You appear to have some details (location of birth Joburg and precise date of birth for example) which should have enabled Home Affairs to find your birth certificate - however, if your birth wasn't registered I regret that is an insoluble problem. I don't think you would have had a SA drivers licence at age 17 when you left for Australia as one could only get that if 18 years old. There must have been documentation required at the Australian end when you emigrated - you could try to explore if these docs are still held by authorities in Australia and if so whether copies are available. Did you attend school in South Africa? May be an avenue to follow up - if the school has records going back to your years there. I am not clear if you have - or had - a SA Passport. Mole.
www.molegenealogy.blogspot.co.za