If we do dua for something and it keeps getting delayed whereas all your other duas get accepted, so does that mean we should keep asking Allah dua that is not being accepted or leave it?

The actual meaning of Dua is to call. Dua is an act by which we get close to Allah (swt) we should always keep in our mind that we are nothing and the one who has all power is Allah therefore we are always in need to Him now our duty is to call our Lord but we can’t calculate which one of our Duas are accepted and which one has not accepted just like a child Who totally rely on his/her parents without any doubt and asks what he/she wants but it is his/her parents has to decide what is better and suitable for their child and what is not good and yet it is not a appropriate time to make his/her wishes true. So we should always remember our Lord by our Duas and this will make a strong bond between Creation and Creator.