Well it depends on the context in which he is contacting you. If he is sending you unwanted messages and calls, you can politely ask them to refrain. The reality is, if you were together for a long time, you were an important figure in their life, and it isn't easy to lose someone you've known for time. So it is important that you're understanding of their behavior as well. If after you ask them to stop contacting you, they continue to do so, stop replying/begin ignoring them. If they do not stop, you can contact the authorities. If you feel the situation merits it. For the most part, with some ignoring, they'll give it up. (They're just broken).