Meeting request updates are not recognized.

In my iphone 6 under iOS8.3, once I have a meeting in my calendar and someone sends me an update with a change in the date and/or time I can not get the meeting to update. The calendar file sent in the new email will still show the original details. In outlook and yahoo the updated information appears. I have tried deleting the original meeting but the update request still does not show the new information. How can this be fixed?