Submit the required document via courier, either in the name of secretary or in the name of the official whose signature are placed on the letter that you received. Once you have couriered it you may call the relevant number which will also be provided under the signature of the AD who has written the letter to you and confirm that your documents have been received.

Donot worry its just a routine thing and not at all anything to worry about, even if you have submitted it already.

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*Whirling Dervaish*