As has already been said, just install the AdBlock extension for Chrome and that will stop your ads. I use Chrome for everything and never see an ad (in Chrome).
I also have a Verizon wi-fi hotspot on my phone and the only thing that gets me even close to going over are a lot of photo and/or video upload/downloads. If you stream any videos, a wi-fi hotspot is not likely to handle it within your data plan unless it has a large limit.
Verizon has been responsive to me when I call them about how to manage my data plan. The last time, they upped my plan from 3GB to 4GB with no change in price and also threw in a promotional update for another MB for a year. This was when I called them when I could not anticipate going over my plan because my phone and their website reported conflicting data usage and neither was correct.
I originally had a 2GB plan that was good for me normally (since I us public wi-fi or my own residence wi-fi for most Internet service). It's only when traveling that I even got close to the 2GB plan. Verizon had updated that play to 3GB for the same price without any input from me.
If you are using any other devices on your hotspot, it may be them contributing to your overage. We also have two tablets and a smart phone with us when we travel and they can do updates and whatever that add up. If you auto upload photos from a phone/tablet to cloud storage, this can also really use up your data if you take a lot of photos.