Put in a written complaint to the Insurers with the pictures, asking them to dispute liability. This is not something you can go to the ombudsman about. It is up to your Insurers to decide on liability, as you delegate responsibility to them under the terms of your policy. It is only if you took this to a court of law, that the Insurers could possibly be overruled.
Problem of proving the other driver at fault, is that you would have to obtain expert opinion or independent witness testimony that the other driver was speeding. On the balance of probability, I would say that it could be viewed as a 50/50 accident. They could argue that if your view was impeded by the transit van, that you should have asked someone to guide you out of the space, by warning oncoming traffic that could not see you trying to exit your parking space. Having said that, in your picture the transit van is not parked right next to you, so if they were driving at 5mph, they would have seen you and the accident could have been avoided.