Flipkart — To change my mobile no to my address no

Address:

Near Hotel garden (Prem Nager)

I want to update my postal address mobile no to my account login no - i did a mistake some months ago when i was i punjab so my prepaid sim card was not working there - so i add my postpaid no to my flipkart account to get call from delivery boy - but when i can came back to my home town in Jammu i trued to go back to my previous no but now it say identifier already in use - i want to chang my no to my previous no because the new no i have added is my mom no