I assume that you mean the seat binder bolt. THat is the bolt that holds the clamp to the seat rails. If this is the case I recommend removing the seat post form the frame and then drilling the head off the bolt. you can then use a vise grip pliers to remove the bolt shank form the clamp. Go to you favorite LBS and have them get you a new bolt or have them do the work for you.
THere is a reason that they put torque specs on bolts. You just learned why.