Aruna,
I design the same report but it was not displaying the customer credit limit, instead it pulled the bank account credit limit for each individual bank account to the field and displayed it as not assigned,.
So therefore we might be using the error credit limit data source. I tried to create a new key field called credit limit but I was not successful. I have searched the system for any other credit limit data sources with no success.
I would advise that you create an incident with SAP, and the will respond as it's not mapping correctly for me too.
Sorry that I cannot be of more help to you.
Regards,
Emeka