Em, this sounds quite strange. I do hope you can get it sorted out...
During my maternity leave, my compnay was also bought by another (larger) company. Approximately half of our staff were offered our same jobs but with the company that bought us, and the remaining people were offered jobs within the compny that previously owned the company. Hope that made sense!

Anyhow, from what I understand from some things I read at the time, your maternity leave entitlements should transfer over and so should your years of service. If your job still exists, then you are still entitled to have your job back, and this includes with the new company. If your job isnt there they should be offering you something as close as possible to it. If this isnt possible, then they have to make you redundant. Have you any idea whether your colleagues are being offered jobs? If they are, then it might be an idea to ask why you are missing out (because they cant not offer you something just because you are on maternity leave - its discrimination - but if there is genuinely no position then thats different).

Give the Workplace Infoline (the federal one as i think thats what you are covered under in VIC) and see if they can give you some advice. I've spoken with them quite a few times and they have been pretty good at telling me stuff.