I had issues with BTinternet when I was living in the UK. No problem with installation but with them doubling my Direct Debit payments without permission. The first time I complained, I received an apology and payment reduction but they did the same again a short while later. This time I was passed around Customer Services for a number of weeks (e-mail) and predictably, not one assistant had an Anglo-Saxon name. It took more than a month after closing my account to receive a refund.
Sorry to hear that your mother is on the blunt end of their customer care, Melchett. It's not that you've even got the option of visiting BT shops anymore and complaining to someone face-to-face because they've all been closed down.