Update:
Application of 8th April on self-care portal was cancelled.
Made a fresh application on 13th April by visiting the local BSNL office. When I enquired y'day, I was told that along with BB plan change I have requested for New Modem acquisition as well, which is totally absurd as I only applied for BB change. They acknowledged that the "Order" which was passed by Commercial department was erroneous.
Now I have to wait for another order which was generated by them y'day to be processed.
It seems BSNL is still stuck in "Office-Office" type situation.