Deducting issues

I am very disappointed in fnb ... i missed my loan paymnet in january and made arrangements to pay ... they did deduct for 2 months but kept phoning me im in arrears and need to make a payment .... so i went into the bank and they descovred that the money was deducted but was not allocatead to my loan but someone elses loan after a long time it was allocated to my loan ... this month they deductetd the arranged amount plus the amount that was outstanding for my arrears and still want to tell me my account is in arrears after a double deduction on my last arrears amount