First off at my work we wear branded shirts as a mandatory requirement and I’ve requested multiple times that I need a size up in shirts but my manager says that the size looks fine to her but I don’t want to be washing my shirts every day. With this she has complained that I should tuck my shirt in and button up the top button but it is physically impossible with the size of shirt they have provided. She often complains in front of customers and it makes me feel embarrassed yet I cannot get a larger shirt for whatever reason.

How to make her understand that my shirts DO NOT fit and that I require a larger size otherwise she can't complain to me as theres nothing else I can do since we can't wear our own shirts.

EDIT: I am new to the company, existing (older) staff have been apart of the company when they used to hand out more shirts so they have the correct sizes and more than 2. now they don't order them even on request even though it says that, if your uniform does not fit, ask for a different size in the staff room.