New number not activated for OTP

I wanted to link my device in order to pay with my discovery miles in store.Only to find out that the OTP is still being sent to my old number.I “supposedly” changed this 3years ago!Obviously the person then didnt do their job. I then AGAIN phoned the call centre to get this changed and the guy said it takes 24hours to activate.Its been more than 24 hours. ITS STILL NOT ACTIVATED!!!!!!! I will not waste my airtime again to get this done as its obviously not happening Now what now Discovery???????? Can someone who is actually competent please contact me to get this sorted!!!!!!