Si I got the refractometer and did the test. It shows 30° but it's a false result. No way it has such high alcohol level, I could not drink it. My dad says it's because it has sugar and the refractometer can't measure it correctly.
There's another chance as my dad has another tool, those ancient ones, like those mercury thermometers. That may give me a more accurate result, so I'm going to test that, when I go to my dad's.
Thanks for the info, 30% sounds a bit too much indeed, would be closer to Rum than Martini :D