I'm sure I need not point out that it seems contrary to Citroen's goal to offer the cashback savings that's no-so-coincidentally the same as London's congestion charge.

You lost me.  What is Citroen's goal other than to sell cars?  

By promoting this technology, they're (not coincidentally) sending the message that they're environmentally conscientious. By telling the public that they can now drive in downtown London without worrying about the cost of congestion pricing, they're undercutting that message.

But yes, of course, you're right. Their goal is not to be environmentally conscious, it's to sell cars. Poor choice of words.