Taking my money twice in 1 month and no refund is possible

Absolutely dissatisfied with my experience.

I wanted to change my debit order so I don't have to keep on manually paying when the debit order bonus. A consultant said that I would have 2 pay twice as that would mean my account arrears if I change the date. On one salary I cannot afford to do that and stated this. Last month I got a call from agent to ask again if I would like to make the debit order change and I expressed my concerns. He said they will not debit my account twice and I can change the debit order. Now its the 1st of the month a my account has been debited twice. This is completely not okay and puts me back financially. This is like theft! I'm so upset and disappointed. I called an agent today and she was not helpful. Not okay!