I used to work in a call center for a cellular company. We dealt mostly with 'business' customers, but they were still just as horrible about basic stuff like that.
I remember one customer that called in and wanted me to get rid of $2000 in texting overage charges that her daughter racked up in a ONE month period. They tried to weasel out of it by claiming that they were supposed to be on an unlimited plan, but there was nothing in the account about it and they refused to go back to the store that supposedly set it up and have them put a note in the account about it.
That was the only issue I had to give up on. I couldn't fix that myself and tried to send it up the chain to management, but they ignored me no matter how many times I asked, so I eventually just 'forgot' about it and left it there.
Was still unresolved when I left that job.