Xiaomi Announced at 9/2/2018 that a new Global Stable ROM is released that fix a major problem with Calling Issue (interrupted call) that reported by many users in Spain, Israel, and Greece.
Bellow is Xiaomi Announcement
Many users from Spain, Israel and Greece have experienced the issue of calls being interrupted or incoming calls are unable to be answered. To resolve this issue, we have released the MIUI version V18.104.22.168.NAMMIEK for users from above three countries and regions. After updating MIUI version, please reboot your device to apply that.