"Inventory error"

I placed an order for shoes that were on special (R400 off) on Sunday. Monday morning I got an email saying my order was cancelled because "an inventory error" and they didn't have my size.

I checked on Wednesday and it still said it has my size.

I called Thursday to find out if they do have my size and they said that they do have my size but cant guarantee that if i place the order I will get it. They also insisted that I pay the full retail price even though I originally placed the order at the sale price.

Very unfair. Why should I pay R1200 when I originally paid R800 for the same thing and not be guaranteed that there isn't an "inventory error" again and not get what I paid for.

Never buying from this company again.