How many times would you contact someone who didn't reply back?

If you send someone an email, they don't respond, then you follow up with a text and they still don't respond even after 2 months. Isn't it the case they got at least one of those messages, and just didn't care enough to respond?

I've been told to just keep sending messages to the person, but that seems like harassment to me. I don't want to harass someone with constant messages if they are not replying. That is not me and I don't do that.