bit late this, but this can usually happen if BT puts a block on premium numbers.
The pitch goes "Do you have kids? or lodgers? we can save you money by blocking calls too premium number and selected telesales/vote lines, you can save upto £2 a minute on call charges". It all happens so fast and is worded so gloriously that people think "coor what a good idea", and tend to say "yes" too save £2 a minute on call charges, not realizing the reference is to Premium numbers and NOT there actual call charges ;)
Then 2 months down the line, realize they cant vote on BB, or order that george forman they saw on Pricedrop TV.