What's a good way to tell a colleague to stop sending me messages constantly?
What kinds of messages are they sending you?
They're messages about work and projects we collaborate on, but they're very controlling and most of them are unnecessary?
I'm sure you're frustrated because these excessive messages are a waste of your time. Be direct with your colleague and tell them how you feel.
I'm sure they won't listen to me, they tend to do whatever they want anyway.
Insist that they listen to you and if that doesn't work, talk to your boss or human resources about the situation. You should not have to feel stress at work because of a co-worker.