Running specials without have the required stock on hand

Dear Shell

Yesterday and went to fill up my tank at your Shell Boulevard Service Station. I was handed a flier for the specials you were running in your shop and decided to buy the 2 x Liquifruit special. I was then told that they do not have stock of the free glasses.

I phoned your customer care this morning to inform them and was told that your supplier does not have stock and that I would have to pop in again at the store to maybe get the glasses as it is dependent on how long the stock last.

As a client I expected that you would make some effort to ensure that I get the glasses as I have already "paid" for it. Now I'm told it's on a 1st-come-1st-served basis. This is not acceptable for me.

If you do not resolve this for me I will stop using Shell as my preferred fuel provider. The service at this station is also not great. I only fill up there for the Clicks points and drive past 2 fuel stations to get to this one.