incompetence resulting in double payment

A representative from RCS has contacted me to inform me that my account will be debited for double my installment amount because they did not action my request (debit date to be moved) as I had asked at the end of November. Instead RCS had removed the debit order instruction!! This resulted in zero deduction for December and so my account now reflects \ ARREARS". I get a call to indicate that I have to pay double the amount because of this.The lady rudely told me that I have to check my phone and if the RCS debit order did not come off my account"