Trending @Capgemini; YER Rating discrepancy

Hello all ,

I discussed ratings with my previous people manager now he left the organisation and he said the rating is 2 and I am very confident that it was given 2 and my supervisor is also confirmed as discussed last week once those ratings came out. Now I created a ticket on AskHR the. My HRBP person POC they provided and initiated the mail chain but now HR says this rating is given on the final basis now we can't change..is this so ?? Or we can fight back to this matter pls confirm guys