In reply to Hassan Khaled:
You only need one instance of the interface internal_sig_if, created by the bind construct. Remove the explicit instance of internal_if. Then the set statement should look like
uvm_config_db #(virtual internal_sig_if) :: set(null , "*" , "internal_if" , dut. dut_if_int_sig) ;
You did not show where the dut module is instaicated; you may need to change that to the proper instance path.