On 26 May, I paid in full for a tractor that was on Gumtree and arranged with the seller that I would be in touch regarding the pick up. Last night, I received a text that said that the sellers have decided they have changed their minds, and want to keep the tractor and will refund my money. I have paid in full and I want to keep the tractor. Am I legally in the the right under Australian Consumer Law, or are they able to get away with this?