Issue with 2-for-1 special offer

So here is what happened. On 6 September 2018 Faithful to Nature was running a 2-for-1 special on Theonista Kombucha. I opened their website, saw the ad and clicked on it. Some of the items were greyed out and out of stock, but I selected one that was available and added it to my cart. When the parcel arrived, only one bottle was included. I complained and Kayleen rep**** that "you've placed your order at 22:12:15pm and the special ended at 21:56:09pm".

I find this response ridiculous. During the checkout process, after I have added everything I wanted to my basket, I had to enter the voucher code T2N to qualify for the special offer, and even at that time, the special was still available and the offer was app****. Right up to the end of the checkout process, I was put under the impression that I qualified for the special. At no point did the system inform me that the special was sold out. In fact, even on my invoice, in the payments section, it shows "Discount (Theonista Kombucha - Buy 1 get 1 FREE, TN2Y)".

And yet, very conveniently, you just say sorry, but the special was sold out. So is it normal for Faithful to Nature to show on my invoice that a special offer was app****, but then it is not?

So here is what I want. Either you send me the bottle of Kombucha, or you come and collect at your cost the one that was delivered, because when I placed my order I did so under the impression that I was getting a 50% discount per bottle!

Please sort this out. I must say, this whole thing left me quite unsure about the ethics of your company!