At a prior employer, we noticed that there were many customers getting essentially free service ($100-200 per month) by calling customer service hundreds of times per month and asking for credits for all sorts of things. They were generally very nice and just picked up $5-10 credits until their service was free. Beyond the free service, they were costing the company the expense of the service calls.

We started routing all of them to a small group of agents and flagged the accounts so the agents would deny them pretty much every time. It was kind of funny because we didn't tell them anything changed, but you could see that some of them noticed because they started asking which call center they were talking to. They would immediately hang up and call back over and over and just keep going back to the same place. Eventually most of them gave up.

Note: nobody here would/should feel sorry for this particular company, but I still thought it was funny to see these scammers get mad that we caught on to the scam.