Can company change appraisal policies without informing employees

My previous company delayed appraisals and PLI for 9 months, by end of 9 months on 31st Dec’17 they shared mail stating the values of my arrears, PLI and increment salary (applicable from Dec’17 salary), also stating that next appraisal will not happen on Apr’18 , but instead will be extended to Oct’18. It was also mentioned that arrears in salary appraisal and PLI will be provided in next 3 months due to financial stability. I received my increased salary on 6th Jan and post that I dropped my resignation letter. Seeing that people are quitting they introduced a clause that if we quit before Apr’18, company forfeits arrears and PLI (Post my resignation).My company didn't inform when I left what FnF will be, they said it will be shared after 45 days. But the amount I received is the salary only, when I asked abt arrears, I was told this clause has been introduced. which I was never informed about. So what are my legal options here, and by when should FnF ideally be processed.