State Bank Of India [SBI] — credit card noc & closure letter

I had cleared the complete outstanding amount on my sbi credit card (Zero balance) and raised the request for closer of credit card, issue for noc and update the cibil repot. My credit card no [protected] when i called sbi customer care for issue noc, every time they are saying that, noc will be reached to my mailing address in 1 week.
As of now i did not receive such letter or communication from their end. It became very difficult thing for me.
When i had paid complete outstanding on that credit card….. Why they are not able to provide noc to me.
Please do the needful..