Like all London councils, Newham have responded to your informal reps with the usual Fob-Off letter, because they know that >95% of people then cough-up, not wanting to risk the full PCN penalty, and, needless to say, thinking that the council know more about the law than they do. Experience of this forum is that councils do NOT know the law and some make it up as they go along judging by their refusals.
So really you have to decide whether to follow the 95% or stand your ground.