"Sit on the cat, not on the dog."
Translation:बिल्ली पर बैठो, कुत्ते पर नहीं।
"Kutte" can mean the plural of "kutta" (both in direct case) as well as the oblique case of "kutta". Here it's the latter due to the postposition "पर"—you cannot say "kutta par".
I agree about the posposition, but we have been using कुत्ते for all the plurals so far.
why is it नहीं instead of मत ? since it's imperative i thought मत would be the prefered one
Billiyaan (cats) is plural and would go without a postposition. Billiyon would be with one. But in this sentence we only speak of one cat. Since billi is feminine gender it doesn't change its form before a postposition.