You can dispute the charge.
In doing so the charges are held - which includes the lower amount payable.
If they find that you do not have a case, you then have the option to pay the lower amount.
I did the same in London - I entered a box junction - there were road works ahead which I didn't realise and the two lanes of traffic wanted to merge into one. It caused both lanes to traffic back into the box. Due to the fact I was stationary they charged me, although I tried my hardest to dispute the charge.
Once they confirmed I was still in the wrong, they said I have the option to pay the lower charge, rather than it increasing to the higher value.
Put it in writting, with your photo's and they will freeze the charges.
Good luck - you'll need it !!