As long as she can speak clearly, write “Hello, I am [insert her name and surname here] and I would like to have 1571, and I am handing you over to my son, who has my full authority to deal with this matter on my behalf” on a piece of paper, and have her read it out when the NowTV Broadband people ask to speak to the account holder.
They need only to be reassured that the account holder is present and you are duly authorised as her proxy, after which they can deal with it by speaking to you.
Though if you don’t have a POA, now is the time to get one, while she still has her mental faculties, as it’s a nightmare to get one if she loses them, and you have to apply to the Court of Protection.
Can you please raise a New Post for this, as it is not related to the thread you have posted in?
A more detailed description may be needed also.
If English is not your first language, can I suggest that you describe your issue in your native language in Bing Translate, and then post the English translation in your New Post?