Nothing to worry about Guddi...
This is just a minor mistake. They might be acting so fast that they forget to attach the file
Most of the times you receive any emails from CIC, you cannot reply back as they are for sending emails out.
I think now you have 2 options to reply back to them regarding the missing attachment
1. Email: Email them using the on-line URL that was provided to you when you have received your SA
2. FAX: Write some cover letter with your file number and mention that you have received an email from NDVO dated:--- and in the email it is mentioned that see the attachment, but there is no attachment in the email. You can ask them to resent the email with an attachment.
I think you can also print the email that came from NDVO and can fax the same along with your cover letter