1) When they turned off my service a month after I moved into my new place, because they had somehow gotten the "moving from" and the "moving to" addresses backwards, despite repeatedly confirming this when I went to transfer service. I honestly don't know why it ever worked in the first place.
2) When they turned off my service when they suddenly decided that my modem, which was purchased new from Amazon and had worked for more than a year previously, had a MAC address associated with their low-income program and couldn't be used on my plan.
3) When their system forgot my account exists (I literally had to create a new one), leading to me being unable to pay my bill.
However, they usually don't listen to the end user stating what procedures have already been completed. It seems like everything would fair better if they just pinged the modem the moment the user identified themselves to get initial diagnostics.
They absolutely shouldn't do this, but I bet that the vast majority of issues they handle are indeed the customer's fault.