These words differ a bit semantically in the two languages. Jeszcze can be translated as still in a sentence like "Jeszcze tu pracujecie" = "Wciąż/nadal tu pracujecie" (You still work here - but soon you won't).
In general, to avoid confusion, better use still = wciąż/nadal; yet = jeszcze
then you should really see control this exercice. as I had them wrong I had them both back one just after the other at the end, so I am sure of what I say. Besides, I had now three times the same problem: when giving the right answer, it is rejected: I do not know how to post a screenshot, I even tried to convert it to pdf, and I leave it, maybe posted you can see someting /Users/dunemariejose/Desktop/Capture d’écran 2019-03-14 à 23.12.10.pdf
The only thing I can check are the standard answers and they are correct in both sentences. So this seems to be a technical issue, only the developpers of this site can fix. If they had a screenshot, they could try and work on the problem. Unfortunately, there is no way I can help you directly.