BILL

I have a contract with Telkom, on the 20th September I went to change my debit order date from 25th day of the month to 31st of the Month. the lady who assisted me at the store advised me it will only be effective from October 2020 because I came late. On the 30 September they debited their money from my account. My problem is on the 4th of October I received my bill via email from Telkom for both September and October as if they never received their money end September the bill included a fine because my debit order bounced. My issue is 1. If they were able to get funds on my account on the 31st why did they add September amount on my Bill? 2.Clearly the debit order date was successfully changed why are they still giving me a fine? Telkom must fix this