Debit wrong amount and cant answer me why

I switched my debit order date from the 26th of the month to the 2nd of each month.the 2nd November they debited my account with R364 instead of R799.i phoned them and they told me I am up to date.I phoned again the next day to hear and the other person told me I am R799 in arrears.he told me that the R364 was because I changed my debit order date.when i querried why it is that ammount for a date that i moved 1 week he could not answer me.he said the are going to escalate the the problem and the will phobe me back in 2-24 hours.it is now more than 2 weeks.i sended them several e-mails(#***,***,***).hope they can phone me back with an answer now.