Unauthorised billing

I bought furniture at Joshua Doore a few months ago. I declined to pay by debit order and agreed to pay the monthly installments in cash. On the 23rd of the month I noticed that a debit order went through, without my authorisation. I went to the branch and requested them to remove the debit order. It was not done. Today the 13th of December thet tried to deduct an installment from my account, but because I only get paid on the 23rd, there was not enough money in the account for it to go through. I was notified by my bank in advance that Joshua Doore is attempting to deduct a debit order and I should deposit funds into my account. I then tried to contact Joshua Doore, but the debit order still went through. I never authorised any access to my bank account, now they deduct as and when they please. My account is not in arrears, as every other deduction went through. I will definitely not recommend buying anything from this company.