Can't sell my 1st gen car?

Hi I have a zentorno since the Ps3 days and I have 2 of them cuz back in the day it was the 1st car I got from the shop, I bought one and didn't knew I had to wait for it to show up in the garage so I bought another one. I never really cared about it but now it doesn't make sense to me to have 2 and I kinda need space in the garage (I don't want to buy another one) but I can't sell them. It says I can't sell those cars. I've tried it with another 1st gen cars that I bought back in the day and it says I can't sell cars over 50000 or something. Can anyone help?