I downloaded this file: http://download.apks.org/?server=12&apkid=com.android.providers.calendar&ver=4.4.4-a1d45e8141
EDIT: This is for Android 4.4.4. If you have another version of Android just do a Google search for the apk file. Then, get it from a site you trust. Also, I have android 5.1, and it still worked, so there's a possibility that it might work if you have a newer version of Android.
Next, I installed the apk file from the downloads folder.
Finally, I downloaded a /system/app mover from the Google play store (requires root), and made the calendar storage app a system app.
I rebooted, and now my calendar works perfectly!