Made regular ptf and terminated

I was made regular ptf within 90 days and there was an incident (the incident was I called a supervisor a clown and was asked to be sent home, he then made up a lie saying I threatened him, multiple letter carriers made written statements saying i did not threaten him) with a supervisor where they suspended and terminated. The union rep filed a grievance and trying to work with the manager at that post office for me to return to work which he refused. It was then sent up to the B team and my union rep is saying they will probably uphold the termination because it’s in my 90 days even though they made me a regular ptf employee.