Quick to Bill (& Collect via D/O), but not to Cred

At my advanced age, moving to an iPhone was a big deal, but Zamani was the intrepid salesman! Great interpersonal skills, but lacking in other areas of knowledge (see below). A few months after the purchase, I advised him that I was going overseas, but didn't want to be billed - what must I do? He told me to go into Settings and put Cell Data on OFF, as well as Data Roaming on OFF. Received a bill a month later for R173. I queried it with Zamani, who told me to go to the Eastgate Technical section. Yeah right! Easily an hour's wait. I decided to rather have the R173 debited with my usual payment run. February saw me again overseas (lucky me!) and AGAIN I went to Zimani at Eastgate. He assured me there would be no bill. I repeated the process. Guess what? A R303 bill. Spoke to Zanele, then Palesa, then Sibusiso - over an HOUR on the phone - and they referred me back to Zimani, whose manager, they say, must help me. Aren't you all part of the same company, brand, organisation? Don't you care that I have been with Vodacom for the past 23-odd years? Apparently not. If the Vodaworld guys escalate this, it will 'take months'! I was supposed to put Voicemail on hold! No-one told me!