This is my profile Ingo.
Now we get a new contributor Ingo.
This is very confusing not only for me. I do not want that someone else post with my user name. How can we avoid this?
Sorry, this is not an issue to be solved on a single stack of the network. If at all it should be addressed all over the Stackexchange network. You will have to take that issue to the main meta page:
Keep in mind though that this problem has been discussed before and the current way is likely by design:
Minor nitpick: it's not usernames that are not unique it's display names. Usernames are in fact unique.
Unless this other Ingo is going to try to impersonate you there is little to be done here. Sorry for the inconvenience.