Hi Abdullah,
Thank you for all your help.
Somehow Sandbox is not working as expected. I did the same in Development and it worked.
I also had to implement an OSS note(2104991 Switch existence check returns wrong results) for an error happened in GENIL_MODEL_BROWSER.
Below is the error.
'Switch ID MDG_BS_ECC_CUSTOMER_SWITCH_02 does not exist'
Now KUNNR field is storing in the backend. Also bringing customer number in MDG UI.
Thanks,
Ramesh