When I signed up for internet, I asked the representative for unlimited data because I was aware of this option. The representative flat out denied that it existed and refused to even tell me the price for such a thing.
It's a relatively new option. It may have actually not existed back when you signed up, or the rep just didn't know about it. Either way, I don't see why they'd want to hide it, because a consistent $50/month fee is much better than a large overage charge here and there that may or may not actually be paid.
It'll be paid. Most of their customers don't have any other choice but to pay it. (Otherwise, most of them already wouldn't be their customers, after all.)