Sorry to say it, but like so many others, you have caused a "satnav assisted" PCN to be served. All over London these restricted streets have been rolled out, and this one is quite new, so unlikely to be recorded on your latest satnav update, and probably wont be there if you do update it tomorrow ! We see cases like yours where the restriction has been in position for several years yet still the satnav ignores it.
What the emergency vehicles could help you with, is if there is an advance sign. This is likely to have been obscured or made very unnoticeable with all the emergency vehicles blue lights flashing etc. So we need to know if there is such a sign.
Claiming you were following satnav wont get you a win at London Tribunals, and the council, evr greedy for your money will refuse your reps, but they will re-offer the discount.