I had a very similar experience when I was very young and had been sent off on my bike to buy a couple of baguettes.

I must've looked totally bewildered; I remember just repeating the phrase "deux baguettes, svp." every time the guy said anything.

Fortunately a kind and patient lady in the queue behind me explained that he was telling me they had none left!

I fled the shop as quickly as I could with a "merci beaucoup" - as if I was kidding anybody by that point that I spoke French!