Servo not working on PLC's PWM(and no issue on arduino)
The PLC's output is in sink mode hence I can't connect it to servo
  directly.I am using and Op-amp OP07CP by Texas in inverting
  configuration


Get rid of the op-amp and use the open collector ouput from the PLC with a resistor to +5 volts.


  please find the attached diagram


On that circuit you show +/-15 volt rails and this could have damaged the servo before you even tried toggling the PLC pin. It looks like the op-amp would deliver a signal between 2.75 volts and 6.3 volts when the PLC pin is toggled so at best you are unlikely to be meeting "0" logic levels.