Well For one, my dealer would never do that. It's not their money that fixes it, it's Nissan's.
And, if you had an extended warranty, they would owe you the balance if they voided it.
I don't think they did, they just said they did to keep you from claiming anything else and,,,, keep the money as if no claims, more for them.
You need to contact the BBB in your area, do all the screaming you can. It's an off road vehicle and you are using it as advertised.
Now, if it is a business vehicle, yea, they can cancel the warranty because it says in the terms that would be a no no (Probably) But, they still owe you balance.
When it comes to Dealers, Never volunteer information. You don't know, you never know .....all you know is it's doing something it is not suppose to do, o, ........... it's not doing something is it suppose to, and that is it! Don't offer, volunteer information. Let them wonder. Name, Rank serial number........
= Last name, Model, Vin. That's it!
Oh and extended warranty's are a bad gamble for you, if it wasn't they would not sell em, The language leans their way 100%