I have just had the same issue there the now.
I'm not on a tariff and my boxes are now classed as 'retired' they are that old yet I'm paying £69.65 per month for them and on a basic package for broadband etc aswell. Due to cost being so high now I'm always getting in to a month's worth of arrears making my bills £150 every 2 months. I called to cancel as BT offer broadband for £20pm and to set up a payment plan for the remaining balance but they outright refused! I have to be a customer to set up a payment plan but can't afford to stay for 3 months to pay arrears while paying current prices. Absolutely shocking to say the least, people offering to pay but being difficult because want to cancel. I intend on putting forward a formal complaint and contacting my local citizens advice as nowhere should decline payment plans to those who can't afford a lump sum, essentially forcing them to continue getting in to debt because refuse cancellation. Surprised virgin still running amount of unhappy customers there are.
Hope you got your issue resolved eventually!
