Incorrect Upgrade Price

I went to the istore to fetch my upgrade which was advertised and shown as R450. I then was told to sign a document for R585 a month and told they will sort this out on the backend. A week later and emails from their management team i am yet to get a response. The call center keeps telling me they are going to call me right away etc. The managers dont respond to emails etc....I cant use the phone until this is sorted out because if anything happens to it i get the bad end of the stick....WORST experience ever should have stayed a Samsung user.