I am prefacing my comment with the fact that I am not an atheist. I believe in God. I also believe that God doesn't exist and you can't prove me wrong on either account because you have no proof either way. Personally, I believe what I believe and you can disagree with me, you can dislike my beliefs, but you can't change them and you can't prove me wrong. It's belief, not fact.
The premise is that the people teaching 'God' are wrong but God still exists. And you are absolutely right, in a sense. When we believe in things we make them real. We have a concept of something which cannot be proven and people believe the concept. Thus, yes. God is real.
As are Santa, dragons, magic, and many other things that a mass of people believe in, but for which there is no physical proof. They also exist because people believe in them. There is no point in trying to convince people who don't believe in them that they do exist. There is no proof and people who believe don't need proof.
I think a better question is why are you trying to convince people that you are right and they are wrong? Who cares that much what other people think about something that has zero impact on our lives. It is a supremely moot argument. Believe, don't believe. Noodles, no noodles. It's all the same in the grands scheme of things.