When you have a public IP, does it mean your IP address will remain the same instead like the private IP which changes every time?

I changed from private to public IP about 2 weeks ago. In 1st week, my IP remained the same. In last 7 days, it has been changing.

So I called Maxis Fiber last night and they told me it will change even if it's public IP. I had doubts.

Then, I just called Maxis Fiber at 12.30 pm today and I spoke to Alex. He also told me that IP address will change even with public IP whenever you restart the modem or every 48 hours. Only business can have fixed IP. You can verify with Alex from your Maxis Fiber help line.

So, who is correct?