On the 1st of August 2023 Sars paid my refund into my FNB account after 21 days of verification of bank details which Sars came back and confirmed my account details are kept

On the 1st of August 2023 Sars paid my refund into my FNB account after 21 days of verification of bank details which Sars came back and confirmed my account details are kept. My problem starts on the 2nd of August wgen FNB takes away the refund without any explanation. Why did FNB take away my Sars refund?