rentalcars.com Bait and switch Manchester, UK Internet

In March of this year I selected a BMW X1 from this company for a two week rental in September in the south of France.  The fee was about $650 CDN for the rental, and I immediately received a confirmation from no_reply@rentalcars.com confirming my reservation, confirming the 25% deposit that they applied to my credit card with a link to my car choice.  At the time, the link displayed the white 4x4 BMW X1 which I had previously selected.  I wanted to have an entry level 4X4 this time in Europe, and this was the cheapest option.

Today I received a communciation from the company which had the same confirmation number as the March email, but when I clicked the link, it was for a Peugeot 508, a sedan. I phoned the company only to be told that the BMW X1 was not in the category I had selected, and if I wanted that car, it would be $1,600 for the same rental period.

The agent in Manchester tried to explain to me:  "Sir, you must understand that a BMW X1 is not in the same category as a Peugeot 508, so it's going to cost more."  My reply was that I was fully aware of that, but from my side, my complaint is that I booked a BMW X1 or similar for the agreed upon price of $650, and OF COURSE a Peugeot 508 is not in the same category so why am I being asked to accept an inferior car?"

I spoke to two agents, both of whom spoke to their respective managers.  I had forwarded my confirmation email to both which confirmed the car type as BMW X1 or similar but they informed me that the BMW X1 was no longer in that category and that as I had booked from the "Standard Full Size" category, they would be furnishing me with whatever was available from that list of cars, which no longer included the BMW X1.

I tried to explain that when they advertized it, and I bought it, and they confirmed that I would get a "BMW X1 or Similar" there was no mention of their category name, and that I do not consider that a full size sedan is in any way similar to a 4x4 and that I insist that they honour their confirmation.  

They refused.  I asked to speak to the manager, and was told that they would not take a call for a complaint that was covered by the standard terms and conditions.

This is extremely frustrating.  If I want to book that vehicle now from another firm, the fee will be at least three times my $650 that I've booked and paid for.  

They won't even take a call to hear my complaint.   What can I do?  I'm furious.