Dear Sina,
In the NREL 5-MW baseline controller, the torque will be computed in Region 2.5 if the generator speed is between the lower (1136.498 rpm) and upper (1161.963 rpm) limits of Region 2.5 and if the blade-pitch angle is less than 1 degree.
I have not reviewed your Simulink implementation in detail, but Leonardo.Lopez uploaded his Simulink implementation of the baseline controller for the NREL 5-MW turbine in the Mar 03, 2017 post in the following forum topic: Baseline NREL 5MW controller on simulink - #13 by Jason.Jonkman.
Best regards,