@Jorge.Sanchez
I am not sure exactly what look you are going for but here are some principles that might help you get what you want.
1. Any polygon(s) can have more than 1 smoothing group assigned. So for example, you can have the chamfered polys share the same smoothing group. But a row of those chamfered polys could also share another different polygroup with the flat side that they border. (I don't know if this is what you want here, but try it out just to see how it works).
2. If you want a surface to be perfectly flat just remove the smoothing groups (Clear all).
3. Once you start manually tweaking smoothing groups, forget Autosmooth. It will likely override what you have tweaked.
4. Something may look correct and is correct in the viewport but may look "wrong" when rendered. I don't have Corona but I rendered a chamfered box in Arnold that looks correct in the viewport, but the reflections of the HDRI lighting in the scene causes reflections that make the box not look quite correct even if it is physically correct. With Arnold this is just the default rendering without any material applied. So if your box looks fine in the viewport but not in the Corona render, try assigning a material with no reflections/glossiness and see if that changes the look.

Hope the above helps you get to where you want, but if not post back the result and any questions.