Population stall (doesn't grow by lowering taxes with room in apartments)

[Pesebrero]

First game ever, not sure if it's a bug, but I'm unable to raise the population. I'm also stuck at exactly 49 children, so I can't build a football ground in order to attract middle class. If I cut the taxes to lower class down to 4% it says "+1 trend" but nobody comes and I start losing money, even if there's room in the apartments (they also have 4 out of 5 level 1 services in range with 100% jobs, but for some reason satisfaction is low).

I don't know what I'm supposed to do, I can keep building things but that just keeps shrinking my income.

[Yheeky]

Hey,
pretty sure it´s not a bug. The lower class trend of course only affects lower apartment buildings. If you´ve upgraded them (in order to build the football ground) they are middle class apartments. Before upgrading all of your apartments, make sure you are prepared to build at least two (better three) buildings for the next class.
To solve your problem you could just build another apartment
Hope this helps!
Cheers, Christian