I'm so sorry your parents are acting like that, that isn't right by any means! You literally cannot just "stop" it's physically impossible. Even people who have overcome their stutters after years of speech therapy have bad days. In fact, the more you let your parents words affect you the worse your stutter is likely to get. Try educating them with articles, medical advice etc. But always remember that your stutter does not define you, you are you, there is nothing wrong with you, there is something wrong with them. Stay strong, stay confident, you've got this. Sending you all the good vibes and support, you're not alone in this.