Sold under False pretences

For my sons 4th Birthday we wanted to get him an electric train. My fiancé went to the Toys R Us in Woodmead and asked the shop assistant to show use where in the store we can find them. He then picked a train and the shop assistant proceeded to sell him batteries. He wrapped the train in the store and on my sons birthday when he wrapped open the gift in excitement and wanted to assemble the R400 train it (to my most extreme disappointment) was not electric at all. I spent the rest of the night in tears because I had been saving for this gift for the better part of 3 months. We went to the Toys R Us at East Point (it is closer to home) with receipt and packaging in hand to exchange the train and the shop assistant told us that because the packaging is damaged they cannot return it but because it was sold under false pretences we can take it up with the store that sold us the train and they will exchange it. Today when my fiancé took the time off work again to exchange the train the woodmead branch told him that they are not going to exchange it because the packaging is damaged. AGAIN I am so disappointed. What did you expect a 4 year old that is presented with a wrapped gift to do other then rip the box? Needless to say that my son STILL to this day (his birthday was on the 12th) has not received a gift from me. I AM SO ANGRY at the absolutely awful level of service these stores are presenting. I am past the point of an exchange. I want a refund.