Thanks for your post and welcome to the community forums. Is this for a new account or for a recent change in service? If so then, this may be your first bill which will always be larger as this bill will reflect the time from the date of the change/renewal and the up coming month. You can find out more here. Hope this helps.
If it hasn't been changed for nearly a year, it does sound like perhaps a promotional discount has ended? I can have a look at this for you to confirm, but I should advise in advance that I cannot renew or renegotiate contracts and packages with you these require speaking directly with a member of the sales or upgrades team by phone.