Discovery Card useless

I have been struggling to change my cell phone number where the OTP is sent to since 3 March. I sent numerous emails and made [hone calls. The last I got was we will phone you back in 48h still waiting. PLEASE READ WHAT THE PROBLEM IS, I explain it every time and Discovery overlooks it. My cell phone number changed. I want to change my banking details and can't receive the OTP because my number changed. I want to change the number where the OTP is sent to. I phoned on 11 March and it was logged. Btw your phone calls are very soft. The person that assisted said I will receive a call in 48h still waiting. PLEASE remember this: my details changed and I could get the verifying questions wrong. I don't know what details are currently on the system. Luckily I got it right the last time but if they ask something is different, they can't change anything.