In order to prove that you are obligated for the debt, Verizon must prove that you agreed to access its WiFi services, and you must prove that you did not.
The fact that you were in Mexico is an issue that I always add to the list of possible defenses, because Mexico is a corrupt environment, both governmentally and in private business dealings, so it wouldn't surpise me if Verizon Mexico were to have figured out that you had a notebook inside Mexico, and then simply generated a bill, even though you did not access the system.
Regardless, this is what is likely to happen: Verizon will not sue you. It will simply terminate your services, and then sell your account to collections. Then the collection agency will sue you to collect. I think that a collection agency will have a very difficult time proving that you agreed to the services billed, because it won't be able to bring any technology experts to trial to testify to how it knows your computer was linked to the Verizon network.
The collection agency could simply ding your credit record and then wait and see if you want to settle the matter in order to fix your credit. So, that's another option.
Unfortunately, you don't have a lot of leverage -- Verizon is not likely to listen to anything you have to say. So, you may just have to stand your ground and wait to see how things unfold.
Hope this helps.
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