Best way to make a hole in concrete wall
Menards and other places rent core drills for large holes in concrete.

Easiest way is to call Diamond Drilling or a similar company and have them come out and drill all your holes for a few hundred dollars.

Unless you want to buy a Hilti DD100 and the bits which will cost you way more than hundreds.

Edit: Sorry I just re-read your post. If you want to cut bigger holes then you need diamond concrete saw blades for a standard circular saw. They will wear down so you could start with 1 or 2 and see how far that gets you. Depends on how many holes you want to make. Hopefully they are available in Ecuador.

Or you could order one like this.

Then you will need a sledgehammer, wedges, chisels, and lots of muscle.

Good luck!