Debit order date change

I have a annuity policy with sanlam. All I want to do is change a debit order because my salary date is changing. Currently my debit order is on the 28th of every month. From next month, I will only get paid on the last day of the month. To be on the safe side, I requested that my debit order change to the 1st of every month. This morning I get a phone call stating that if i change my debit order to the 1st, my next deduction will be double because November will be outstanding? Why? A debit order is still going off? I m at work during the day and really don't want to deal with this. I am really so irritated with always having to fight about everything. Seems to me like everybody is quick to sell policies but have no interest ever in helping a client. I sometimes doubt if this policy is even worth it. Please change my debit order date to the last day of the month - 31st of every month since the 1st is an issue.