An increase of £40 to make it £90??? Seriously? We are already in credit!
It’s just a recommendation. These are not always accurate depending on how much data they have. They are trying to ensure that over the course of a year you cover your bills without any nasty surprises. You are free to decline the suggestion and set the direct debit at a level you feel is suitable.
@bros650 if you have a look at this post there is a discussion on how payment increase recommendations are calculated by bulb. (https://community.bulb.co.uk/discussion/6639/frequently-asked-questions#latest)