How to remove unknow person (not member) from repository? Commit happening with unknow user-name

Whenever I commit my changes to git with user-name “hasing”, the commit goes with name “Ali Atakan Basaran”. “Ali Atakan Basaran” is not member of repository. How to remove “Ali Atakan Basaran” from repository? What should I do, so commit with user-name “hasing” doesn’t go with “Ali Atakan Basaran”? See attachment for member list and commit info.