I think if the service manager told you then and there that it wasn't their fault, then he's full of it. To be sure, he would have had to take the time to talk with the people who actually worked on your car, he'd want to do a little diagnoses on your car to see why the AC isn't working at the moment, and maybe even have a look into the FSM. If he did none of the above, he just wrote you off without a second thought. That sounds like lawyer time unfortunately.
Now that you're a member, you can look at the Service Manual for your car and view the diagrams and make some of your own determinations of the relationship between the CVT and AC systems. Like, look at the removal and replacement procedure for the CVT and see if it involves any of the AC system components. Okay, I was curious and took a look. To remove and replace the CVT, step one is pull out the entire engine and transaxle (CVT) as an assembly! There you go, the entire engine bay has been worked on by the dealership. Unless there's some sort of shortcut to the FSM where you can lift one side and pull the CVT out, which would need to be confirmed with the techs performing the work and whether or not they bypassed the FSM instruction.
All FSM chapters are here
http://www.nicoclub.com/FSM/Versa/2007/hatch/
Here's where I looked at page CVT-207
http://www.nicoclub.com/service-manual? ... /hatch/CVT
Welcome to NICO Club! Please tell us how this works out and Good luck!