Contract sold under false pretences

On 18 April 2015 I took my mother who is elderly, to Vodacom Tygervalley, Cape Town for a cellphone upgrade. After some time deciding on which package to choose (as she has been complaining about excessive cellphone accounts), we decided on the U-Choose Smart S package, after the salesperson above informed us that for the month of April there was a special where all the items on the package is double, ie. instead of 75 min talktime, you get 150 min talk time, in stead of 200 sms's, you get 400 sms's, and in stead of 200mb data you get 400mb data. We soon realised that this was never added to the account when she had to recharge her talk time and also her data as she only got the standard 75 min talk time and 200mb data. After making contact with the salesperson above, he phoned Vodacom Head Office and was told that no one actually got that and that it reverted back to the original smaller amounts. THIS IS UNACCEPTABLE - I AM SITTING WITH THE SIGNED UPGRADE CONTRACT DETAILING THE BIGGER AMOUNTS THAT WE WILL GET.