Kurt Denke's response to Monster was legendary, and can be found here.
Notice that he doesn't admit, concede, claim or offer anything at all. Just asks for a proper claim to be stated, and makes a few salient observations.
In your position, I'd get a lawyer like Kurt Denke to write my response to the BSA.
Blessed be those who initiate lively discussions with the hopelessly mute, for they shall be known as Dentists.