The rental charges are for the upkeep of your line/exchange (bloody rip off IMO) How much do u use your home phone? The rental (non paper bill) should be £10.50 a month.

As BT will take a considerable amount more by default to cover their arse... If your account is in credit after 4 months you can ask then to either 1. rebate your money or 2. take a payment break.