What class did you reserve? I would consider a 2-door Beetle "or similar" enough to a Focus, at least as far as size and passenger accommodations are concerned.

That said, accepting that the Beetle was unsuitable - at the airport, you have the most power of any rental situation because competitors are right there. For next time, I think I would politely ask for a refund, then whip out the trusty smartphone and make a Priceline reservation with a competitor on the spot.