Hello Danstar94.
Please do the following:

Hover over the DayZ card in the Xbox OS, press the start button and go down to "Manage Game and add ons"
Go down to "Save Data"
Delete the save Data for the account with the problem
Select "DELETE EVERYWHERE", the other option will not solve the problem
Note that doing this will close the DayZ client if its running

Regards,
Geez