Incorrect product delivered and order then cancelled without crediting full amount!

I placed an order for a 3D pen - blue as a gift for my daughter. As it apparently needed to be ordered from the supplier it had an extended delivery time. On collecting the pen on Saturday it was the wrong colour. I immediately logged a return request and stated I wish to receive the replacement urgently! This was, after all a mistake on there side. I contacted the call centre and was informed due to the fact that the return needs to be logged and inspection needs to be done as to why the product was delivered incorrectly, I can possibly only receive the replacement in 2 to 3 weeks. I then received an email a short while after, stating there is no more stock of this item, however if I search on the site there is more than enough stock, and I have been credited to my takealot account. The amount now credited to my account is only the product purchase amount, not the delivery cost. So now, I have basically paid takealot a delivery fee and still no product!!! How on earth can a supplier get away with such bad customer service time and time again?