Mishandling of saved money

Good day

I have a savings account with Capitec bank for over 10 years and also have flexi saving accounts linked to my savings account. Last Friday someone sent me money to my Capitec account which I then transferred to one of my flexi saving accounts to use at a later stage, this morning i received the following message Capitec: Your savings account has a negative balance. We app**** set-off, which means R965.73 was debited to account *** and R965.73 credited to account *** to partially recover the negative balance. Outstanding balance: R46.27. Info ***. I called the number in the SMS and was told that I owed Capitec on one of my flexi saving accounts for a purchase that was made in 2016, to my surprise I asked the consultant/agent how that was possible as you can only swipe purchases from your savings account and not from your flexi saving accounts. She then said they will escalate the matter and she will call me back, but I have heard nothing from them until now. All I want is my money back and clarity as to how I had a negative balance on the flexi saving account which is a sub account.