Line rental increase charges???

[#1]

I have just had an email from plusnet saying that line rental charges will increase from 23rd September and I will see new charges on my bills after that date.
As I paid for my line rental annually upfront how can plusnet now decide to charge me more for something I've already paid for? Or is this just a generic email sent to all customers?

[#2]

As your line rental is paid for 12 months up front that part won't affect you.until it comes up for renewal
Have a read here http://community.plus.net/forum/index.php/topic,129255.0.html