I had credit card when I lived in australia with a bank there while on a holiday visa. I left 18 months ago without paying back. At this time there was about 7000aud on the card. If I was to return to Oz would I be tracked down for this?

I am surprised they have not tracked you down in another country? But if it was 7000, and you have all the late fees, most likely legal fees, I would guess it is at least 10,000 or more now