Errr... It's bad when my head think in Spanish and my fingers try to type in English...
I try to re-write the whole thing, maybe this time it makes more sense.
I was unable to get the score of 45000 required points because at higher levels, I always get killed. I tried to stay at the lower levels so, even if the score obtained for each babelian rescued is lower, its safer for me because there are less flying vees and no firing UFOs.
I.e., in level 2: I rescue 5 babelians, then I allow the aliens to abduct 5 babelians. The counter of Babelian rescued is 0/6 again, and I can stay at the same level all the time I want, just avoiding to rescue the sixth babelian. Then I continue like this, rescuing some babelians (+200 points each) and allowing the aliens to abduct some more (-50 points each), always increasing the score and being safe enough to not lose any of the lives.
As I said, it takes a long time, and a lot of patience is needed, but eventually you can get the 45000 score.