I drove an NHS hire car through Ring road in East London  where congestion charge sign/warning was not on the road but on adjacent roads, on 28th July. When I received a warning from the hire car company, I had to pay £17.50 the following day because to avoid any penalty even though I believe I did not enter the zone. I tried to see if I could check anywhere online if I had entered the congestion zone, no luck. When I spoke to congestion charge team, they said they could not tell me either.