April 2011 I went to have my sons great grandmother claim the both of us. Considering we lived at her home but she got rejected because someone has done used mine & my sons ss#...
What do I need to do to see whom claimed me & my son?.

She needs to file the return MANUALLY (mail it in).

When the IRS comes back to you to check on whether she can claim them, be ready to PROVE that she is eligible to claim the dependency exemption. Once that proof is given, then (and only then) will the IRS process the return and grant her the exemptions.

They will then go back to the OTHER person who claimed them and DISALLOW those exemptions, demanding payback of the taxes owed, plus penalties, plus interest. The other person may even have to explain themselves to a judge at their trial for tax fraud (though, admittedly, that IS unlikely).

Unfortunately, IRS privacy rules will prevent YOU from ever finding out about who that other person may be, at least from the IRS.