Cell number not recognised for ecomm purchases

When doing online ecommerce purchases your bank brings up a page where you must authenticate yourself. The process is called 3DS. You enter you cell number and it sends you an OTP which you must enter on the website. For the last 2 months I have been receiving an error message that my cell number is not the same as what is on the system. Then I must use my email address instead, which means I must always be home and at my laptop to perform any online purchase. I have called IB and CArd Div, I have logged complaints on the SBSA website and nobody ever gets back to me and the problem persists. What the HELL???????????????????????????????????????????????