New cellphone number info still not updated

I have had a new cellphone number for months now, and I have been into the branch on many occasions to update my details so that I can make payments (OTP is still being send to my old number). It is ridiculous that I need 2 phones in order to make a payment. I want to sell my old phone, but not if the new owner is going to get notified of my every banking transaction. Please can we sort this out once and for all.