When making the case that the limits aren't realistic, you should first find out how much your using. Both what Cox says, and a alternative method to fact check them. This shows the Cox way, though its out of data since the page redesign, should be close enough. You can break it down by month or week, so it should give you some information to start with.
As for the non Cox way, what kind of router do you have? It may have a way to check usage there, and might even isolate what computer is using the bandwidth and when. There is also free software you can use to monitor your use.
Once you know what your usage is, and have confirmed its accurate, and its legit, and not a virus on your network or something else fixable, then its up to you to see how much more you need. If you find Netflix is taking up too much, you can adjust how much it takes. See here more info.