Is it better to call the personnel manager or send a text message?

Don't even think about it. Call and ask, of course. You can call directly to explain that your original intention is ok, and I can edit a version for you:

Hello, Manager X, my name is XXX. I attended an interview for XXX position in your company on March 23rd. You told me that there would be a specific interview time in the second half of the year, but I haven't received the notice yet, and it's close to the end of the month. What's the arrangement here? Will there be an interview in the near future