Right.
OK, I think I got it this time.
1-Click "Internacionales"
2-Click "Cajas y Encomiendaz"
3-Click "Caja correo"
4-Scroll down and click "Retiro a domicilio"
5-Scroll up and click on "Sistema track and trace" (on the left in blue)
6-Looks familiar right
Ignore "T&T plus" link and click on one of the three links in the "T&T" box below. I'm 99% certain you want the one in the middle but if that doesn't work try the other two. It has the RR prefix you were talking about and I believe the package is from Argentina to Australia right, point of origin to abroad.
There you go.