Upgrade misrepresentation

On 29 April, received an email from MTN to upgrade and went to the Menlyn store to do the transaction. I took the email with me but the assistant, Bianca,couldn't find the offer on her system. I forwarded the email to her and she forwarded it on to her manager, Owen, and MTN themselves. One hour after having sent through the query I received another email, same as the first one but with a note that they had made an error and the price was in fact double. Bianca said that it would take no more than 48 hours to get feedback on my query. Without any clarity I went back to the store on 10 May and the store manager, Owen, stated the MTN will not honor their initial offer as they admitted their mistake. Riana Mall from Customer Value Management was Owen's contact with the matter but I do not have her contact details to take the matter further. The CPA protects consumers against false representation and MTN cannot simply say sorry and assume that this makes things right. I went to the effort to go to the store and do the upgrade and the offer was in force at the time. Any store will always charge the shelf price for an item when getting to the till regardless if it was a mistake on their side and MTN must do the same. I was stonewalled in the store and fear that my query will get lost behind red tape if I try reach MTN via telephone especially since I already waited 10 days to be told that they will not help me anyway. Regards. Stuart