debit date change

In December I contacted FNB home loans Dept to request an eraly ded as I got paid earlier than my normal pay date. they allowed the change and debited on the 18/12/2015. on the same date i requested that they chnage it back in January and debit on the 27th which is the initial and normal deduction date. to my suprise yesterday i got an sms to say they debitted my account and i had to make a plan to get the money so my account does not stay on a minus. Please can someone contact me to confirm that this has been fixed and that my next ded will be on the 27/02/2016 since they took the January debit order already