Increasing payments when in credit?

I am currently more than twice my monthly payments to bulb in credit. I am told my payments need to increase by almost 20%.
WHY?
I thought industry standard was one month credit was sufficient …

Based on average yearly usage and recent price increases Bulb has advised customers of a rise in direct debit payments. If you are meeting the required minimum of one month in advance and are in control of your account then it is possible to adjust your direct debit payments on line. By going to “your account”

Bear in mind there has been a price increase and we are coming in to the colder winter months, many customers will have built up credit during the warmer months to cover this.

Have a read at this. Payments and statements: