How to tell my dad to stop filling in sentences for me?

How to tell my dad to stop filling in sentences for me? It really annoys me! Sometimes i ask a question or say something and he thinks I’m done, he fills it in for me. When I tell him to please let me finish, he reluctantly says okay and kinda gets mad. For anyone it’s annoying when your sentences are completed. He says that he cannot tell if i am done or not when i Am talking. I tell him it’s because i get stuck and he just has to wait a couple more seconds and look over and see if I’m stuck. I don’t understand why he gets mad. It’s not a personal attack or trying to make him feel bad, it’s about trying to ensure the best experience for the both of us. Talking to him makes me nervous so can someone help me find links? He won’t really listen. He’s very stubborn (just like me) and thinks that he knows what he’s talking about. He thinks the experts don’t know shit. But, he’s wrong. Thanks in advance!