1st Birthday Ruined

We ordered a reversible trike for my son's 1st which is today and the item arrived yesterday. I assembled it this morning and it was not very safe or secure for him there is no strapping and in the reversed mode(which we bought it for) he is tilted so far forward is almost falling out. I immediately called their number and explained the situation. The lady was incredibly rude and said that because we assemble the item it would be considered used and they don't accept returns on used items, furthermore we would have to pay the courier fees and the return price will be less. On top of all of this she went on to insult us and say there must be a problem with him or us as no one else ever complained about the product. Furthermore when I asked to speak to Morne Nel she said the email I got from him was just and automate email and I can't speak to him nor can I come to the store I must just email them and accept their terms. This is absolutely pathetic customer service and a shocking experience for a 1st birthday...