Absa takes money then says they didn't get it.

my car payment was debited for my vehicle finance of my account and it was not returned on my side. I keep getting harassment fron absa vehicle finance that it is unpaid for March. My statement clearly shows that the funds were taken off my account. In all the time I have has the vehicle finance this has never happened. Standard bank says the money was taken, absa says they never received the payment. I have all the proof to show absa has taken the money and in all this every day I get harassed by absa. Who is at fault here....