There could well be grounds for submitting representations and also an appeal at London Tribunals, but we need to see the video. Looking on their website, one can only view the video by entry of a web-code that is on the postal PCN. I can't see one on the front page, so it must be on another page somewhere. Please advise code, or download the video yourself and post it here.
The photo on the PCN shows you turning left into the restriction, so there really should be an advance warning sign; is there one ?
Google Street View latest is May 2019, and doesn't show the restriction, so we really need to see some photos taken by yourself, if this is possible ?