Help needed with Realms (Freeradius) Urgent!

Currently I have my multiple realms up at proxy.conf up and going but everytime I do a radtest my user is able to authenticate with the multiple realms  which I do not want to after stripping the realm.

e.g. abc@company.com   : login ok
      abc@company1500.com :login ok

Is there a way to just "bind" the user abc to auth to just company.com and prevent cross authentication.

Any help is appreciated or does anyone know how to specify a user to a single realm. Thanks