I don't think there's any penalty for false accusations of copyright infringement. Likewise, nobody needs to pay for falsely accusing you of anything unless you sue them for defamation.

If your ISP actually cuts off your internet after 6 false accusations, you might want to take them to the courts. EFF will probably love to take on such a suit. Unfortunately, very few people have the financial means or guts to sue the RIAA/MPAA and follow through with it.