Promised top up data not honoured

I took a contract upgrade and asked the consultant that according to my usage what would be the correct package. I was informed that there is a special on that doubles up the data. I then up graded and was told only one month is doubled but was told it is for the duration of the contract. I have not been given the data and when queried was told there was no promotion, until I found the original advert , when I was then told it was only for one month and not the entire contract duration. No where on the advesimemt does it specify that the double data is only for one month.I have been chasing this issue for a month with no result.