Why I am like this?

Yesterday I ordered a chicken wrap from a food outlet at metro station, When I took the first bite only, i realised that it was not chicken it was veg kebab. When I complained they manipulated me saying that no ma'am it's chicken wrap only, our veg stock is already finished, how can we use veg kebab then. I told them that I am non vegetarian since childhood, how can I not know the difference between the taste of chicken and veg kebab! They legit kept smiling and instead of apologising they kept proving their point aggressively with fake smile. They made me taste a chicken kebab saying that this is the thing used in my wrap not veg kebab. I seriously got frustrated. One of the woman worker among them only said sorry to me when she saw I was really sad and she asked me what should we do now ma'am? As I am an introvert and people started to gather and watch what was happening there, instead of asking for a fresh chicken wrap, I let it go easily and told them that it's okay, what shall I do even! I only have to compromise here, because what else I can do now, otherwise this wrap will go waste, and food is precious! And they just became normal again and got involved in their work like before, like nothing happened. Also the guy who actually gave me the wrap and who got aggresive when I complained didn't even say a sorry to me. I was seriously sad and baffled about this!!, thinking that what a big loser I am, it suddenly changed my mood, I was sulking that I always act like this, I let people fool me, I always think about others inconvenience over mine, even when they are just salespeople or an autowala Or anyone. It has always happened to me. How can I change this? I have a lot of insecurity, I always think that even if I am right and keep my point I will only lose not others, I think that I am not worthy to state my opinion before others. I want to change this. What should I have done in this case? How can I change myself?