Change of ownership after my mom passed away

I have been struggling to find help since March. My mom passed away in Feb and I am trying to not lose the number and have it moved over to my name. I initially went into an MTN store in Bayside Table View and spent 90 minutes there giving them all the documents and proof they needed to do this. They told me everything was done and the account was moved over to me and the debit order would go off my account. This didn't happen and the money continues to go off my mom's account. Then I phoned MTN call centre and spent another 20 minutes on the phone trying to get this sorted and still no joy. The money continues to go off my moms account and the account still shows to be in her name. What else am I supposed to do??