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Your problem is that you set the wrong CRS - probably the most frequently asked question here on GIS SE. Your coordinates are interpreted in the wrong CRS definition. See here for details why your points fall on the Null island.
For lat/lon coordinate values, use EPSG:4326 as layer CRS. Set this CRS in the import dialog (see screenshot 2) or right click your imported layer, click on Set layer CRS and select EPSG:4326 (screenshot 1).
You wrote you "tried" WGS 84-Pseudo Mercator and WGS 84-Antarctic stereographic. But none of them uses lat/lon coordinates that your coordinates are in. The imported coordinate values must be assigned to the correct layer CRS to be interpreted correctly.
If you want to show your map in Antarctic Polar Stereographic projection, set the project-CRS to EPSG:3032 (or 3031). See here for the difference of project- vs. layer CRS
Screenshot 1: setting the right CRS of the layer

Screenshot 2: setting the right CRS when importing

Your points are plotting at "Null Island", which is the intersection of 0 latitude and 0 longitude. Hence you can be sure the import has not picked up the spatial geometry correctly. As to why, a possibility is that you imported csv text file without specifying geometry, or that you chose the wrong columns, or that the columns are being picked up as text rather than numeric. You might have to share some data or give more information to clarify this.