Will call when I get home. Hopefully they don't take 10 years to answer.
You need to tell them to "migrate" you from TI DO Uncapped Advanced to TI DO Uncapped Premium (avoid any debates about them screwing up). I did this beginning of February and my latest invoice reflects that I was billed for just the Premium account after all the debits & credits are taken into consideration.
Should add that I gave up with the Call Centre and had to visit a Telkom Direct shop where I learnt the magic word "migrate"