I have ordered a climbing plant "Boston Ivy - Parthenocissus tricuspidata 'Veitchii'" from an online nursery in the UK. However, the nursery sent me a similar looking, but very different species "Virginia Creeper - PARTHENOCISSUS ENGELMANNII". The nursery sells both plants online, and the pictures online are listed against the correct plant. I complained and send pictures of what I received, and I immediately received an apologies about the confusion, and a promise to correct the order. To my surprise I received another pair of Virginia Creeper again! I complained again with more pictures, only to be told that what I have received is indeed "Boston Ivy"!
I have tried to explain to the nursery the difference between the two and that clearly what I received is not Boston Ivy but Virginia Creeper. I explained that Boston Ivy leaf has this distinct three sides
and that the Virginia Creeper has the cluster of leafs 
Is there an authority on plant naming that can confirm the distinction between the two plants? They nursery themselves do believe their identification is absolutely correct and I am not sure what is the best way to challenge them in the absence of a real plant identification authority.