Vodacom Cavendish staff very unprofessional!

I visited a Vodacom (Cavendish) store in March to update my banking details, and it was confirmed at the store that the details had been updated. To date, they still debit my old account, surprised when the debit is unsuccessful. What irks me is that this affects my credit report. When I escalate, I am asked to contact the call centre. Why should I duplicate efforts by calling again when I got confirmation that it was done?