Sorry to say that, but your parents are horrible. They have no idea how hurtful these remarks are. My mother said something like that to me once, only once, and i still clearly remember it, and indeed everytime i think about it it feels like a stab in the heart. And it was like 20 years ago... I can only imagine your pain going through this. Growing up stuttering with toxic unsupportive parents generate even more stress and depression. You should tell them about it, tell them how it makes you feel, tell them that they're doing something bad, very bad. Tell them you need support, not mockery. If they still behave the same after that, keep your head up, keep doing what you do, get you independence, and move away. Surround yourself only with understanding and supportive people. I wish you all the best, brother.