Free Traffic Legal Advice

Dear sir,I was issued a PCN for using Silvertown Tunnel northbound,date & time of issue 09.09.25 15.11hrs.I explained I was unaware of a toll to be paid,I'd used Blackwall Tnl many times before,it was free and assumed the same allied to using Silvertown Tnl.I saw no signage to say there was a toll to pay until I received my PCN.I also explained that I felt that the signage approaching  this busy tunnel informing driver's there is a toll is inadequate. They've refused to overturn my PCN & sent me a hard copy Notice of Appeal to send to London Tribunal, it states on the grounds of appeal ONLY 7 examples where an ajudicator can allow an appeal,any other examples of which I've stated would probably be all be in vain. Is there any point on still appealing my PCN,or would it be pointless.
I look forward to any advice or help regarding this matter,many thanks,Steve.