False advertising

I went to mtn in Langeberg Mall, Mosselbay to upgrade and choose the R139/m package with Sony e4. The salesperson took my detail, I signed forms and she said I have to wait at least a week for the phone. When I went back after a week, she said i cant get the contract at R139 anymore, its R169 now. I went to Mosselbay Mall in Heiderand and ask the salesperson about the adverti*****t on their wall still stating the R139/m contract. She phoned someone, then removed the adverti*****t and say I cant have it! When I upgraded the adverti*****t showed R139, how can the say R169 now?