Short receipt of income tax refund

We have received refund amount less than the amount claimed in the return (AY 15-16), Amount claimed in the Return is Rs 21 Lakhs, and Refund received in 16 lakhs. However form 26 AS also shows the amount as claimed by us in return. we would like to know what is the procedure to be adopted for getting the balance amount. IT website should a demand for old AY (10-11) of Rs 4 Lakhs which was incorrect and we had replied to that, now that message does not pop up in IT website, my doubt is whether they have adjusted the incorrect demand with the refund amount. further in this case what should be our response to the department. Please help. Thanks in advance