Calendar events not showing/changing

Calendar events show fine in my samsung but in my mothers phone they never work. First she had sony and I never got it show any events in the widget. Now she has honor 8 and it has the same problem. Mostly it' just stuck with some week old event or blank, no matter what you do.

Is it related to what calendar you use or what could be the problem?

Kustom supports only Google calendar, if that device is not using standard Google calendar then events wont show up, there is nothing i can do unfortunately

Well that explains, thanks for answer.

I use google calendar and still doesnt show.