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Wait 30 days after they received the certified mail for a response. If you get no satisfaction then dispute the one that is not yours as such. If they come back verified then you can either file a complaint with the CFPB or use the ID Theft provisions of the FCRA to get it deleted.
http://www.consumerfinance.gov/complaint/
Did you ever have an account with ING Direct?
I would suggest using the ID Theft provision of FCRA 605B to get those accounts removed if you're certain they are not yours.