Unable to purchase online until price went up.

I have been trying to purchase a Defy 600mm Oven and Hob box set online which was R5299 on a special it kept on saying the was no stock available. The sale was valid till the 11th January 2021 I tried to purchase the box set online before the 11th but with no luck, I tried again on the 11th January 2021 in the morning and it still said no stock available. I then tried in the evening to purchase the box sent when i added it in the cart the price went up to R5999 and now the was stock available. I thought they said the sale was valid till the 11th but then when I tried purchasing it in the evening the price changed and since the price went up there was now stock available.