Ask Adrian: Vodafone keep sending bills for money I don’t owe — how do I stop this?

Question: I cancelled my broadband with Vodafone months ago and moved to another provider. But despite settling my account, I’m still getting notices for a huge bill of €1,488 from the company. I have been on to customer service several times, who told me I didn’t owe them any money and that it was fine. They even sent me a text saying that I would not receive a further bill. But then the next day I got another text warning me I still owed them €1,488. And then I was notified in a follow-up letter that I still owed them that amount. How can I stop these warning texts and notices? — MD (name with editor)