I had a look at this earlier, but you hadn't posted a full-info PCN, so held off. However, assuming it is your car, GSV shows a clear No Left Turn sign, albeit only one. The council have clearly recognised this is an unusual restriction, so have place a Right Turn Only sign in advance of the junction, plus a CCTV symbol: -
https://maps.app.goo.gl/QJYcmkVao1kiwY5f8Presumably you missed both signs ? Or maybe chanced your arm hoping...? In your favour is that on arrival at the T-junction, there is only the NLT sign, with no carriageway arrow indicating direction. I have to say that if this were at London Tribunals, I think you'd lose, unless you can tell us more.
Were you following satnav instructions ?