misleading informfation for sales

Towards the end of November I received a call from a sales agent from FNB cellular,I took a contract for a sony xperia c,the sales agent stated that I would get 1gigs of data from cellc every month which was her selling point.I came to find out that I received 1gigs of data but I can only use 500mb as normal and the other 500mbs from mid night to 6am,this was not mentioned in our agreement.when i called fnb cellular I was told that an agent would call me to resolve this matter it has been a while and I still have not been assisted.This is really unfair,if I knew this condition to the data I would never have took out the contract,and if I dont receive a solution I am definitely going to the FAIS ombudsman