Part of open source is realizing people will steal your code. The only thing you can do is expect them to give the legally mandated minimum of an acknowledgemen

Part of open source is realizing people will steal your code. The only thing you can do is expect them to give the legally mandated minimum of an acknowledgement of copyright and authorship in alignment with the terms of the MIT license. Are they good neighbors? No. Are they breaking the law? Only if they refuse to include an acknowledgement of your copyright in accordance with the license you gave them.