100% invested in retirement

I asked for a pre-retirment LOA due to excessive OT effecting my Physical health, it was suppose to be approved by my upper management, the system is set up where it goes through the first level manager first, so my request never made it to upper management and the first level forged an E-mail informing the system and HR, that I was denied my leave, so I had no choice but to involuntarily resign before I reached 55 which is the early retirement age opposed to 58 in our work group.. I was 100% vested in the retirement plan, put since I resigned one year before I turned 55 the company change my full pension eligibility from 58 to 65 and if i want to take it at 55 or 58 it will be a 10% a year penalty our pensions was frozen,and it was agreed we could take our pension at 55 with a 2% penalty per year up to 58 which I was going to do. and I was invested 100% how can they take away my rights to claim my whole pension at 58 and my retirement medical at 55? Can I fight this? If the Loa would of be approved that by the way was an option offered by the company it would not of effected any of my retirement. Can I fight this?