Arrangement Not Kept by Capfin

This morning on 18 December 2015 Capfin decided to debit the instalment of December 2015. This was not our arrangement. There is a reason why I made the arrangement for the debit to go off on 21/22 December 2015. I know I'm the one that is in arrears and owe Capfin however what is the point of an arrangement then? Is this the way Capfin is treating their clients by debiting personal bank accounts without authorisation from me because I gave authorisation for the debit to go off 21/22 December 2015. THAT'S AGAINST THE LAW! That money that was in the bank account was meant for other things of which clearly I'm unable to cover due to Capfin ********ly debiting my bank account on a day which was not approved by me. I would like Capfin to refund what they've debited and actually following arrangements that was made and agreed upon. Really disappointed at the way Capfin went about this issue. I normally had great service with them. Clearly after paying them I will not use them again. CAPFIN PLEASE REFUND MY MONEY AND TAKE IT ON THE DAY AS PER ARRANGEMENT.