I cannot get calendar invites in my IOS inbox.

I recieve calendar invites in my yahoo email inbox. From there I am able to add the invite to my ios calendar and accept. The problem begins when the appointment is updated. I cannot move the appointment on my calendar. Even if i delete the old appointment and try to add the new appointment, like i did originally, it doesnt work. I use the calendar for work and the 3 people who send me the invites are all on ios as well. Does anyone out there have a solution?