User/Outlook is sending 100+ acceptance emails to the organizer | Remove exchange account in iOS without losing contacts, calender | How?

Job ID: 37338050

Budget: $10 – $30 USD

...a user's outlook is sending out multiple meeting acceptance. The user accepted a meeting request from his phone, I believe it was his phone atleast, and ever since it has been sending 100+ acceptance emails to the organizer of the meeting. The organizer of the meeting have invited me without any problem, but for the user I talking about, the issue persist. Both organizer and the user are using office365.

The user have a newer iOS version than 9. How do I solve this problem? Maybe a solution is the delete the exchange/office365 account in the users iPhone, connected to the built in Mail app and let him use Outlook app from Microsoft instead? If that is the solution, how do I make sure contacts, calender and so on does not get deleted when doing that?

Once again, what is the solution to get rid of the "User/Outlook is sending 100+ acceptance emails to the organizer" problem? Thank you.
Related categories: iPhone Microsoft Exchange Office 365