Change Debit Order Date

I changed my debit order date from the 23rd of each month to the 1st of each month on the self service after the payments were debited in my account and the system showed me that the next debit will be on the 1st November.Hollard has debited me again on the 2nd of October.Please advise my account was debited for my policy payments on the 23rd September 2019 and now again on the 2nd October 2019.This affects my cash flow am even thinking of canceling my service because their system can’t calculate properly.Made the same changes on my AVBOB and Union Life and they said the next debit order will be on the 1 November 2019 because payments were debited on the 23rd September 2019.Am really ****es and disappointed.