Incorrect deal sold to me

I went to the telkom store in chatsworth and the 40gig was on the deal sheet for R149 but the agent could not process the order and said it was most probably a mistake. I needed the Data deal urgently so settled for 2nd best, the 20gig for R99. Now 2 weeks later the 40gig is advertised for R149. In all fairness to me, I believe that telkom needs to change my new contract to the 40gig for R149. Thank you