Extra billing for early payment

I have been a customer of vodacom since 2014 and have been with brand even prior to taking my contract in 2014. So I set up a debit order for my phone which was not working out for me as i had people *****ing money in my account so I altered to paying the account in store which i have been doing since the 25th July 2017 to avoid being charged extra for late payments and the debit order bouncing. So on Weds 4th Oct i receive a lovely sms saying my payment didn't go through to which i called in to be told that their systems have been giving them problems and hence my payment is not reflecting so i must send a POP which i have done and still no changes.

Monday I check my statement only to find that I have been charged an extra R100.00 for my payment bouncing, but funny thing is that i paid on the 27th Sep 2017. Surely this is not the first time i have paid vodacom early seeing as the debit order is due to go through on the last day of the month or on the 1st. I have records showing that i paid on the 25 July 2017 and 28 Aug 2017 and for both statements for AUG 2017 and Sep 2017 I was not charged this R100.00. So why am i now being charged for someone else's mistakes? the system being late is not my problem so i don't see why i now need to pay. If i had been previously charged in Aug 2017 that would be a different story but i was not. Please sort out my billing.

Thank you