Do you have the original confirmation e-mail you received after making the booking (before submitting confirmation number to BRG)? If you do it clearly states it is a refundable booking, just FWD it to the department.

I had Westin in Bali do the similar thing to me. The rate stayed the same but it was changed to prepaid. My cc was never charged though and when I inquired (I called the hotel directly) they said I could cancel without penalty. I didn't have to cancel though so I can't tell what would've happened otherwise.