Mushrooms when didnt ask for them

I just purchased what I thought was a roast chicken pie - the label said chicken pie and when I started eating - I turned out to be a chicken and mushroom pie. This is devastating as I cannot have mushrooms - fortunately after the first bite I realised and threw the pie away - While I was at the till, a gentleman from the bakery came to me and asked me which pie I had orderd, - I told him a roast chicken pie and he looked at the printed label and sent me on my way - obviously the lady selling me the pie is clueless as to the difference - Huge medical issue nearly!!!!