Salary not paid die to unfulfilled timesheet for a week.

I am on permanent payroll in abc pvt limited IT company for almost 2 years now. I work for abc's client xyz. Every month I fill timesheets for both abc and xyz.abc asks me to provide the snapshots of xyz's timesheets every month. The salary paid in March is for the timesheets submitted in earlier month. I forgot to fill my timesheet for last week of March for abc. But i had filled xyz timesheet and had attached to abc. As per abc, I have to fill the timesheets till 3rd April Or else timesheets will not be possible to change and hence no changes will be made in salary thereof. The unfilled days will go as LOP. Not cut from leaves. Also it is true that they frequently send emails of reminder saying the same before 3rd April. I got to know this around 15th May and i requested them to make adjustments but company denied. They send reminder emails but it is not mentioned in policies or procedures which I am entitled to as per my employment letter, to be treated as LOP Can i take legal action and get the unpaid salry back.