I've reduced my energy usage, how can I set my Direct Debit below the recommended amount?

5 days ago i had an expert into my home to adjust my energy usage SIGNIFICANTLY, what OVO are saying i will be paying for the upcoming year is based on my previous usage, as is the normal process, which i fully understand and acccept. However, that means the direct debit amount they're saying i have to pay this year is to cover a projected amount (and potential debt) that is now definetly not going to exist. My usage this year is going to be dramatically lower from the year they're going by, surely i can set my direct debit below the recommended minimum payment!? It's my debt. But as i say, it's not going to exist now anyway. My usage is now going to be much much lower than last year, so setting my direct debit below the recommended amount doesn't concern me! Am i allowed to set it below it? p.s. i am currently in a small amount of credit on my account.