In NeoBT Mobile Banking:

Go to the menu "Products" and tap on "My Cards". Select the card, then select the "Disable SMS Alert" option at the bottom of the screen. Finally, enter the phone number for which you want to deactivate the service. 

In NeoBT Internet Banking:

Go to the menu "Products" and click on "My Cards". Choose your card and select the "Options". One of the possibilities is "SMS Alert". Just enter the phone number for which you want to deactivate the service and you're done!