NTL customers in Swindon face hikes in their bills of up to 40 per cent.
It follows a new policy introduced by the company to standardise its pricing structure.
People across the town are currently paying different prices for their television service.
But now bills that are currently as low as £17 will rise to £24.50.
The increases affect people who signed up with the cable company but kept their telephone bills with BT.
Ntl says it is creating one price for all customers.
And it is effectively forcing people to sign up to its telephone service by offering them a joint TV and phone service for just £22.50.
The company says customers have been fixed on different rates for years because special discounts brought in when people signed up have never been discontinued.
One victim to the price hike is pensioner Margaret Griffiths, from Moredon Road, whose bill rose from £18 to £24.50 without warning.
She was informed of the change by being sent a bill of £44.50 to include arrears the company claimed she also owed.
There was no letter of explanation and no consultation over the change.
Ntl says Mrs Griffiths had mistakenly been put on a discounted rate and that for years she has been paying too little for her cable TV service.
Mrs Griffiths said: "If I'm paying too little then a lot of other people are as well. My niece and my neighbour have both got the same package and they were paying the same amount as me.
"I can't understand it because I have been on the same rate for years.
"Surely ntl can't just change its agreement with me without any discussion or notice.
"I said there's no way I'm paying that I'll just carry on paying what I have always paid until I get some sort of written explanation."
Ntl spokeswoman Adette Sullivan said: "We apologise to Mrs Griffiths for not writing to her before increasing her charge. The computer should have generated a letter when it flagged up her account.
"We will credit her account with £20 to cover the arrears as a goodwill gesture."
She said the anomaly in Swindon has happened because there are so many customers still being served by the old analogue service.
It is bringing in one rate for all, and encouraging people to sign up for both TV and telephone packages.
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