If you didn't go to the next League level and you were in League lvl 51 (While ending the season in the top 8), this means that the server could not meet the requirements for the next League level (52) with the Clubs that were eligible for promotion. It seems that you most likely are at the top level of your server, Jani0608, and there weren't enough other eligible lvl 51 clubs in other lvl 51 Leagues that could be promoted.

This is something that the devs are aware of and we're working on improving the player experience at those high club levels.