They're just blowing you off or they don't know what they're talking about. It's not up to Apple to implement Carplay on their systems, it's up to them to do so.
It has taken years for the first OEM CarPlay systems to start appearing. Hyundai is just now getting round to it with the Sonata, and Chevrolet and Honda are finally putting in CarPlay compatible systems.
It is extremely unlikely that the head unit in your car would be upgradable to support CarPlay. You're going to have to replace the head unit entirely to get it more than likely.
Keep in mind that aftermarket systems do not have a good track record so far. The first Carplay units from Pioneer were not designed to Apple's specifications and stopped working with later versions of iOS as a result. Pioneer has publicly stated that those units will not be updated and have essentially been abandoned.
Systems supporting Android Auto have not had a much better showing in the market.
It takes years for auto manufacturers to implement changes like this. As much as I love the idea of full integration of my car with my phone, I'm not holding my breath. The automakers want their systems to be closed and proprietary. There is no way they can keep up with modern mobile technology and the rapid update schedule for mobile device operating systems.
