I used to work for a call center for a major cell phone carrier. Many of our customer service calls were the result of the salesperson being poorly trained, irresponsible, careless, or worse. I saw people set up with multiple plans for one line. Many people thought they were given a "free phone" for signing a 2-year contract, but they were actually on an installment plan.
I had one customer call to see if she could cut her husband's plan back to save money. Through smalltalk as I worked, I found out that she had visited one of the retail stores to try and get help. She explained that her husband was in the military and was just stationed overseas, so they would not be using the phone for a year. The store said they could not help her because she had signed a contract. There is a clause in the contract that allows those in the military to pause their service at no penalty if they are called for service. If she hadn't called, she would have been out $600 that year for no reason.