Does it never work, or suddenly stop working? If former, check the phone's APN setting https://www.publicmobile.ca/en/on/get-help/articles/set-up-data-on-an-android-phone
If later, it is very likely the data has been used up. You should have received SMS saying that.
Perhaps you're viewing outdated info on the website.
Issues are common with Public Mobile’s website, which displays outdated information, to deal with this: