Vitality account incompetence

I have spoken to the accounts department more than 8 times to change my banking details and each month they debit the incorrect account then phone me to tell me my account is in arrears, which I know because the debit went of the incorrect account. I have even have them confirm that they have the correct details and still they take it off the wrong account. Now I am the bad guy and I have to pay for the return unpaid debit order. I am so sick of this.