If they actually did this, it would be the exact oposite of net neutrality:
https://www.savetheinternet.com/net-neutrality-what-you-need-know-now
Net Neutrality means an internet that enables and protects free speech. It means that ISPs should provide us with open networks — and shouldn’t block or discriminate against any applications or content that ride over those networks. Just as your phone company shouldn’t decide who you call and what you say on that call, your ISP shouldn’t interfere with the content you view or post online.
Without Net Neutrality, cable and phone companies could carve the internet into fast and slow lanes. An ISP could slow down its competitors’ content or block political opinions it disagreed with. ISPs could charge extra fees to the few content companies that could afford to pay for preferential treatment — relegating everyone else to a slower tier of service. This would destroy the open internet.
So IF the isp was actually traffic shaping or blocking, it would certainly not be "enforcing net neutrality".
But, it looks like the OP just maxed out his monthly cap, so it has not much to do with net neutrality in the end.