Just to add my two pennies worth...
From my point of view, yes the wheel sizes are correct, but when people say that the the tyre dimensions are clearly visible I have to disagree.
Say a Nissan garage fitted the wrong set of tyres and told you what size they fitted, would you complain?
Of course you would, because you know what the correct size should be.
But, if you were unaware of the correct tyre size and the traction control issue had caused you to have an accident, what then? Who is to blame?
You for not knowing the correct tyre size, especially when you went up in wheel size?
I don't think so.
You are buying from a trader that is supposed to know what they are doing, after all they claim themselves that they have been in business for about 10 years,
it's fair to say you would trust their knowledge.
Personally, I would approach them saying that they got it wrong and it's not the first time.
Ask them if THEY are willing to take responsibility for someone, should they have an accident because of wrongly sized tyres.
Tyres are the only thing between the car and the road, so you want to know for sure you have the right stuff and be able to drive with confidence.
As a consumer I think you should complain (politely) and ask them to put it right.
Mention that trading standards may well take an interest, since this is not an isolated case.