When a participant writes an unpleasant, bossy, or snooty inquiry about their account, I respond with:

Your inquiry is important to us.  I am unable to locate the account with the information provided or there are multiple listings under the same name.  So that I may review the account and provide accurate information, please respond with the full name of the account holder, the last four of the social security number, and the name of the employer.

My professional, articulate equivalent of “Who dis?”