Unavailable Price?!?!

I bought a bluetooth mouse from Takealot, making payment. I was emailed an invoice and I thought the deal was done. A couple of days later, I recieve an email stating my order was cancelled. When I called to query I was told my mouse is no longer available at the advertised price and I would have to pay the full price for my item after I have been refunded. I feel this very unfair as I paid for the item at the price which was advertised and I shouldn't have to fork out R300 more just because the item is no longer available at the price originally advertised. Anyway who has time to call Takealot everytime when making a purchase to verify the price.