After I set new DAVdroid connection application suddenly shows message “…was deinstalled” or “…is not installed” or something like this.
And really, application is missing. I restarted S7 and try to reinstall it.
This is probably some problem of your device. Did you move the app to the SD card? Are there any anti-virus solutions etc.? Custom ROM? DAVdroid does not uninstall itself (this is not even possible), so there must be some other problem that leads to DAVdroid being uninstalled.
But I have only one option: buy it again via Google Play store. It is not acceptable.
We have absolutely no influence on Google Play and how it works. However, Google never charges twice, so you don’t have to be worried about that. For more details, please contact Google support.