Until recently I was a Verizon Wireless customer. Their website is a complete mess. Typos everywhere and I would encounter exceptions every visit. Many times I would encounter loops in their flows and never be able to complete a task. I very frequently had to call in so that a supervisor could just force through what I needed.
And that’s just the front end.
I completely agree with you, the back-end billing and other processing is probably a nightmare. From professional experience I can say it can either be quite manageable, or nigh impossible, to make small changes like this depending on how shitty the foundation is.
I think the ISPs are overdue for a complete overhaul but they can’t/won’t because there is no market or regulatory pressure to spend the money. They literally don’t care how shitty their services are.