If you are with Octopus Energy (I am and I didn't want to be), and you disagree with the increase in DD payments that they suggest, just reply to their email politely requesting that you pay £xxx per month and that you have good reasons to want to pay that amount.
They responded within 3 minutes of my letter and agreed to allow me to continue being "in the red" with my payments.
Here is what I sent to Octopus Energy...
Please be advised that my DD payment must not exceed £112
I have tried to adjust it to £112 today and failed.
I do not really want to exceed this amount as in the past you have owed my family more than £1000 and getting that back off you was so difficult it took my solicitors more than a year to achieve a satisfactory outcome.
I would quite like to be in the position of owing you £1000 for one year, to redress the balance, hence my reluctance to increase my DD payments to the amount you specify.
Should you continue to withdraw more than £112 per month, I will find a better supplier.
Thank you,
<<JefO>>
PS If you cannot authorise this, then forward it to your superiors.