Mondo wont return the money they debited after cancelling contract

My husband took a contract with Mondo with the hopes off building his credit score. he then cancelled the contract before the debit order date and Mondo still debited his money. we have been calling Mondo for the past 4 months and being transferred to different Consultants that have been giving us stories. They now want a bank statement showing they debited when they know very well that they debited money. we are being told again to send a bank statement after all these months and that we will have to wait for yet another month.