Policy deviation by employer

Dear Sir, I have worked in one company for almost 5 years. I left the company on 24th March 2017 by serving the notice period as per company policy. There is one policy called performance pay(PP). PP is very subs part of the salary in this company. As per PP policy if employee is not on company payroll as on 31st March then employees is eligible for PP as per last performance rating ( which is A in my case). However company is not giving the performance pay on the ground I was covered under the appraisal process and I am rated D, so no PP. That means company is deviating it's own policy. Please guide can I file a case against the company for this deviation?