Account DEBIT 3 Times

I called the call centre on the 03Oct2015 to make an arrangement for the debit order I missed. The person I was in contact with confirmed the arrangement for an additional amount will be debit from my account each month for the next five months. On the 24Oct2015 my account was debit and on the 26Oct2015 my account was debit again for the same amount and for the additional arrangement amount. In total my account was debit 3 times. I want the money for the double debit to be reversed back into my account today (27Oct2015) as an arrangement was made for the shortfall amount and I stuck to the agreement.