Using WhatsApp because in Germany there's no way around it for public contacts.

Edit: I'd love some response on downvote (as always). I use other messengers myself as an avid foss fan and techie and even had it uninstalled a while. That was until I went back to participating in social life and I sure as hell can't get institutions off of WhatsApp as totally frustrating and idiotic as it is for them to use it in the first place.