Vodacom Monthly Debit problems

Called Vodacom well in advance to change my banking details for the September they test and assure that they have been chaanged for the month end debit, but they still use my old banking details and the debit bounces costing me R75 with my old bank, i speak to Thakiso to change the banking details she checks and comes back and advises me that the new banking details were effective but she doe not know why the ran the debit on the old one for end of September, They now run another debit from my old account for the end of October, and it now costs me R100 because it bounced back,I now owe my bank about R175, please help and advise me on how i will be able to recover the R175 i now owe my old bank.