I have data in an unknown projection to me.

I open it in QGIS and I see that the shapes are ok, but I need to identify the projection in order to merge this data with other stuff.

The points look like WGS84 (EPSG:4326) but without comma.

If a point in WGS84 is like this: (-58,-34)

In this projection the coordinates are something like: (5670000,6120000)

Any ideas?


EDIT:
Here there are three pics, showing the situation.

This is the data I'm trying to import, that i don't know what is the projection. Look at the point marked, it corresponds to the central square.
![Data I'm trying to import][1]

This is my data (it is in lonlat even though it looks deformed). The coordinates shown are from the same central square.
![My data][2]

This is google maps showing also the central square coordinates.
![google maps][3]


  [1]: https://i.sstatic.net/3YnUL.png
  [2]: https://i.sstatic.net/F88zA.png
  [3]: https://i.sstatic.net/R6im2.png