In one of my team i have already played a level 6 CL whend i was at level 5, but there was only a level 6 team in each group, all the other were level 5.

The probably reason is that you need 8 LEAGUE of a creating level to create a CL draw, since only the first 4 qualify for CL, and you need to create 8 groups.
I dont belive that you have 8 level 27 leagues in most servers, majority of the managers give up before level 10.