The PCN still has the 0870 number on it, indicating Bristol CC still get money from the call charges thus exceeding the penalty demanded. As far as I know this has succeeded now quite a few times. Of course, with TPT not having an on-line enquirable register of cases, it is difficult to investigate, unlike the register at London Tribunals. For me, this is a scandal, but there is nothing in law to force them to do it.
I don't think there are any other appeal arguments.