Payment allocated to wrong loan

Hi finchoice just made my account in arrears after I called the call centre yesterday and the agent said they will rectify the mistake in today still meaning yesterday...I've explained to her that I have a flexi loan and kwikadvance loan...so when I made a easy pay payment on Thursdylay the payment was allocated to the wrong loan it was suppose to be for the flexi loan now my account is in arrears which is going to effect my credit score ..please finchoice rectify because what the use you call the call centre and they say it will be fixed but you rather end up in arrears