Just phone them up on 0191 5013601 and say you don't really think you can justify the increase in cost. If they start veering towards cancelling you with no questions, pull them back by saying you enjoy the service but that extra £3 a month adds up over the year.
Eventually, they should offer you £7.50 a month for the next 6 months. If not, then just come out and ask "are there any sort of special deals I can get?".
