If you find that certain people are finishing your sentences for you when you stutter, ask them to not do that. I’ve found that some people do this with good intentions, they think they are helping you out. Most will stop when asked. If they don’t stop when asked, politely tell them that they are being an a**hole. You can workshop that. If your work/friend environment is healthy, there should be someone there to back you up. If there’s not, then I would strongly consider moving into a more healthy environment if possible.