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I worked in project A for about a year with a Manager X before I moved to my current project B with a Manager Y. I work in a physically different geography, in fact different country and don't see both the managers face to face.
When I moved out of the previous project A, I clearly stated to the manager X that I want to discuss about my performance appraisal as I am moving to another project (and under a different manager). X agreed, we had a discussion and he said he will rate me "N" in the scale. The conversation ended that he will note this N into the company's Performance Appraisal Tool when he moves me to a different project so the new manager can rate me accordingly.
After couple of months, when the actual performance appraisal rating was out, I got "N-1" rating, and I was taken aback and shocked. I approached the new manager and requested that I would like to discuss as this was a very short time for him to evaluate me and the new goals need to be on the tool. He instead of discussing directed me to talk to the previous manager.
I tried to talk to my previous manager by email, phone and chat, he never acknowledged back and looks cold to my communication. My HR is pressing me that this needs to be accepted within a week. I am seriously stuck with this approach of my manager and Unfortunately in our company there is no 360 feedback. Please advise, should I escalate to his manager or HR or just blindly accept this rating considering that this can turn worse.