Poor poor service from this company

I have changed my banking details with blue lable in the month of of November. To my surprise I received money in my old account that I have using with them, they went and debited money from the wrong account. I cannot reverse the debit order or even stop it. I don't understand why when I was amending my banking details last month why was the old debi check not canceled. I called their customer care number, spoke to a lady by the name of Sana who could not assist with with anything,I told her I want the money to reversed back to my account, she only told to me email them my bank statement. I requested to speak to a manager, the lady kept me on hold for close to 10 min while I was holding. She did not bother coming back to me after the phone hanged up. I really cannot wait for to finish paying them off. Once my contract is finished. I am canceling this contract.