First, test whether your OIS really works or not. Open camera app then rotate your device in an instant manner, if the viewport still moves, it works. Do it for all axis as it can be partially broken. OIS can't eliminate all shakes, only reduce it (to a large degree, though). When you're sure it's not working, get CIT app from MIUI 7, there's an entry for OIS calibration. Some people say it doesn't work across reboots but in my case, it is. Even across ROM upgrade.