Change of billing accounts details

I had a simple query of changing bank details and the first time I went into the branch I asked if I could change it online or over the phone and the consultant insisted I come into the branch with only a bank statement and no other proof of address document. She was adamant about how I could not change or update my details via electronic means. I brought in my statement and was advised that the next month it would go off my new bank account. The next month it did not go off the correct account. I went back into the branch with another statement and the consultant updated my documents and again insisted the next month it would go off the correct account. On 20th July, it AGAIN went off the wrong account. I contacted the call centre and the lady said no details had been updated on her side. She didn't even listen to what i had to say and kept rushing me to finish what i was saying so she could ask me questions.