Just to clarify and double check everything:
In your GTA V root directory you should have the ELS.asi, the ELS.ini, possibly a ELS.log file and a folder named "ELS".
In the folder named "ELS", you should have another folder named "pack_default" and a text file called "@ INFO.txt".
Inside of the "pack_default" folder, you should have another folder called "@ UNUSED", a text file called "@ INFO.txt" and then finally all of your .xml files.
You should have nothing else inside of the folders mentioned. The .ini must stay inside your GTA V root folder.
Make sure the .xml files have the same name as the ELS car models found in your game. I've personally replaced the core-game cars with new models, so mine are in a mods folder and called police.ytd and so on.
Once you're confident all of those are correct, check the ELS.ini file to make sure the option called "VcfContainerFolder" is pack_default.
Let me know if that works, good luck