Telkom debited my account 6 days before the agreed day

I have a standing debit order for the last day of the month and Telkom decided to debit me on the 25th of December and there was obviously no money in my account because I get paid on the 28th(December or not). Now I have a double invoiced for R5700 because they decided to change the debit date without my knowledge. Secondly I get charged r105 for all bounced debits and this happened because I don't have money on the 25th as I get paid on the 28th. Please fix this. Your service level is very annoying.