I am astonished that you knew nothing at all of the expanded ULEZ scheme which has caused enormous controversy and has been in the national press many times. The expanded ULEZ is the area of land whichh is the responsibility of the Mayor of London, so whilst it doesn't cover all roads within the M25, it gets close !
Signs on approach to London on the A23
https://maps.app.goo.gl/jLFDMme4LjKSRkpi7and
https://maps.app.goo.gl/mt3FEbomgbE4vGer5and
https://maps.app.goo.gl/ZYM7sdXQ5JaUh1Ea8Personally, I think these signs are a complete disgrace, but they are apparently legal. You can, of course, after having representations rejected by TfL, test the matter at London Tribunals, but I have to say you would be taking something of a gamble.
Also I would have thought your friends in Carshalton Beeches would know all about it and have told you about it. However, we are where we are.
So I would send in representations against the two PCNs you've received, and say that although you now understand that you entered the ULEZ zone and having stayed overnight, received two PCNs, you were not aware the zone covered Carshalton Beeches, and you passed no signs that you recognised as a low emmission zone and the need to make payment for non-compliant cars. You should state that you accept you entered the zone, but consider that two PCN penalties for a first offence is disproportionate and request that the second PCN be cancelled. They may cancel the second PCN if you are not confrontational in your representations. YOu would then have to pay the discount on the first one.
Other point to make is that there may well be a 'technical' appeal based on TfL mismanagement of the enforcement process, but I'm not the expert on this, so wait until others contribute but don't miss the deadline for payment or representations which you'll see on the PCN. Such an appeal would be tested at London Tribunals.
Of course, if you are willing to risk the full penalty (2 x PCN penalty), you could take them to London Tribunals on the signs issue, and also, potentially, on the technical aspect of the PCN itself.
