Make an official complaint that they made fun of you for a protected disability that you have. Whether or not you personally consider your stutter to be a disability, for a lot of people it is, and we need to stand up to that sort of discrimination. There’s simply no excuse for that. If I were you I would raise hell; negative reviews online would be least of it. I would make an official complaint, talk to the manager, email the company and inform them that discrimination against customers based on a disability is unacceptable. Do that so that the next kid who shops there doesn’t have to deal with the same bullshit.