I've checked the Course of Sales data. There was indeed a 50k...

I've checked the Course of Sales data. There was indeed a 50k trade at 0.044 ($2200), at 12:05:32PM, on ASX. But there was a 50k trade at 0.045, at 12:22:20PM, on CXA - presumably yours. A later ASX trade at 0.044, at 02:43:45PM would have reset the latest price to 0.044 [or ASX might have reported 0.044 throughout]. It's unlikely, but even if you put in your Buy order before 12:05:32, someone else's order could still legitimately have been executed first, eg. if they also were in earlier at 0.045 or higher, and a 50k Sell at 0.044 came in. So your 0.045 looks legit, but if you think you might have a legitimate argument, I suggest you start by taking a copy of the Course of Sales data.