Bad service

After being a loyal customer with Vodacom for many years, I am currently fuming and considering my options with regards to migrating my number. A few days ago, I received an SMS advising that my contract was up and I was eligible for an upgrade. As I am currently in Johannesburg, I went to the Vodacom shop at The Glen. I sat down with one of your assistants, Keneilwe (?) Morake and advised that I wanted the exact same phone that I had as though my battery wasn't lasting I was happy with the phone itself - an iPhone 6 and I didn't see the point of paying the extra required for an iPhone 7 or 8. I asked if they had a silver available and Keneilwe went to the back to look. After being away for some time, she returned to advise that they only had dark grey available as all other colours had been discontinued. I agreed that I would take this phone if that was all that was available. She explained the new subscription and provided the forms. She advised that they were just the standard forms and just told me where to initial and sign my name. I then paid the R150 for the upgrade and left. Upon arriving at home, I realised that the new phone was a 32GB whereas my phone is a 64GB. I returned to the Vodacom shop as I wanted to change it as this wasn't the same as my original phone as I had requested. Keneilwe said that I needed to talk to the manager but it was his day off and I needed to return the next day. I went back the following day at 17h30 and Keneilwe told me that the manager only worked until 17h00 and I needed to return the following day between 09h00 and 17h00. Today I returned to return the phone and hopefully find the manager in. The manager, Thabang Masilela, advised that this could not be done as I signed the forms. I explained that the request was always to have the same phone and that size did not even come up as an item in the discussion. He then said that 64GB aren't manufactured any more and that all the iPhone 6 stock was just devices that Vodacom are trying to dispose of. I once again explained that this was never discussed and whilst I was told that the different colours had been discontinued, the space never came up. I then said I was happy to take an iPhone 7 and pay the subscription difference. Thabang said this was not possible and that there was nothing that I could do to return the device. He denied there was any responsibility by Vodacom or Keneilwe because I had signed the forms, regardless of the fact that I requested the identical phone and that the size of the phone was not discussed. If Keneilwe could advise that the colours had been discontinued then why did she also not advise that the different sizes had been discontinued? From what I gathered from Thabang during today's conversation, it isn't that the colours/sizes have been discontinued, just that it is old stock and this is what is left. I am now being told that there is nothing that can be done and I must just be stuck with an unusable phone. Why on earth would I want a phone that is half the size of my current one. I think the service is ridiculous and the lack of accountability deplorable.