Experience & releiving lettet

I worked with Lucknow based company Encardio Rite as I&M Engineer in Delhi Branch office 3.5 years from 1 Nov. 2011 to 31 May 2015. For giving my Experience and Relieving letter company want Rs.8000/- from me against serving short notice. However I served my 3 month notice period from 1 March 2015 to 31 May 2015. But during these 3 month notice period i took 28 days leave. 5 days leave in march, 10 days leave in April and 13 days leave (4to9May'15 then 12to16May'15 and 22&23May'15) in May'15. But I served up to 31 May'15. During my notice period I had 15 Earn leave(EL) but they didn't adjust. For each and every leave they deduct my salary during my notice period. Now they did 5+10+13=28days(leave)-15 days(EL)=13days~short notice~=Rs.8000/- As per my appointment letter: "After confirmation, further service with the company will be terminated by 90 days notice in writing from either side or 90 days salary in lieu. No pending leave can be adjusted against this notice period." My points are: (1)I had given my resignation in writing on 25 feb. 2015. (2)I served my 3 month notice period from 1 March 2015 to 31 May 2015. However During notice period i took 28 days leave. But I served up to 31 May'15. (3)No pending leave adjusted against this notice period. Should I pay that amount or not? Or Should I use lawyer's Notice?