Best answer by Duppy
Welcome to the community.
Yes it is certainly possible to increase your direct debit payment.
Go to your account via app or website, go to the menu ( 3 lines top right ) go to help, ask Wattbot, start your message with message the team and explain that you want to increase your payments. If you can work out how much you are underpaying each month and how much you want to pay off your arrears each month, you can suggest an amount you will be comfortable with.
Replies are not instant usually within 24 hours.