Discord is bad because it's centralized. So I would recommend something like simpleX, which protects your privacy. If your friends don't want to use it, then you need better friends because they should understand that you care about yours and their privacy.

As for real-time calling, that uses UDP, which is why something like Tor can't do it, since it's a TCP-only network, so either you need to find something that will let calls work over TCP, or give up on the idea of real-time calls and switch to voice messages, which can do over TCP.