Failure by Bidvest Bank to change mobile number

Good day. I opened an account at Bidvest Bank and gave them my mobile number. Few weeks later I changed my mobile number. I then asked Bidvest Bank to change my mobile number in their system. They told me that they had updated according to my request. I received sms to confirm my request. Till today I am still waiting for sms notification to inform me of the activities in my bank account. All sms notifications are sent to my old number. I do not understand as to why a bank can fail to do a simple change of mobile number.

Regards Zolani Mngqithi ***