I work in the Billing Disputes department of a large landline phone company. The vast majority of disputes that I process are related to third party charges. I'm just a peon, so I can't speak for the overall philosophy behind allowing third parties to bill on our bills, but I can say that once we are notified that a customer doesn't want the third party charges, we do place a no-charge block on the account, and refund the past 90 days worth of charges, with no discussion. There shouldn't be any back-and-forth between a customer and the phone company, the charges should just be removed.
On the other hand, I have run into many people who actually DO want 3rd parties to be able to charge on their phone bills, especially WOW players, since that is a pretty popular payment option for that service. The problem we run into in these situations is that our block is a blanket 3rd party block and will block both their fraudulent and legitimate charges.