Inaccurate information provided to get customers to sign up

Their ad on the radio sounded very promising about saving you money so I thought I contact them to see what they can do regarding my car loan. Received a phone call and started providing the required information as requested. The lady who assisted me gave me an amount that I will pay monthly and what my cashback will be if I go ahead which was a saving for me so I went further ahead with the application. After filling all the documents and submitting them, the lady came back to me and said the banks approved the documents but gave me a different monthly payment and cashback. When I asked how is it possible that the price changed, the lady stated she said plus-minus and that is what the banks are offering. How is it possible that you can give a customer an amount they will pay and then suddenly change it and not just by R300 but more so inaccurate information is being given to lure customers in and sign up for refinancing etc.