Account settled but bank debited

Account number : 003113 I have made debit order arrangement with Lewis to pay my cousins account via debit order. Which I did untill the 21/08/2020. I went to the store to settle the account on the stated date and therefore requested my debit order to be cancelled. But the store manager refused based on that the account has another installment which is being paying by hand by the account owner. The bank was debited on 15th 09 2020 for an account installment which is settled on 21/08/2020. Please refund me my amount which I settled and continue debiting.