The next stage, if you don't pay-up, is the Notice to Owner. Are you the owner, with your name and address on the V5C Registration Certificate ?
Only after you have had reps rejected against an NtO, can you register an appeal at London Tribunals. Greenwich will most likely re-offer the discount, but there isn't that option at London Tribunals, and to be honest, your argument has been tested there before and rejected. Having looked at the evidence, I don't think yoy'd win, sorry to have to say it. If you'd parked on the opposite side of the road like the other cars parked there, then you'd have been in the clear