Poor service

Hi I have been calling FNB call centre several times no one is responding I went to the branch yesterday they told me to reverse money on my banking app, I transferred money on the 25th to my personal loan cause I wanted to pay them in advance however on the 26th they deducted the amount again I went to the branch yesterday to ask for assistance for reversal but they told me to wait I then waited and when I try to dispute the debit order it says “the debit order cannot be disputed contact your banker or the number on the back of your card” this is poor service cause they cannot take money as I already transferred the outstanding balance for this month