The real problem here is that after this stunt I'd like to completely stop using Whatsapp and switch to something else instead, but I can't because other people use Whatsapp and communicating with other people is essential to me.

So, switch to something else and convince a few other folks to do the same (e.g. "I am not available on <whatever>, use <whatever++> if you want to talk to me"). Y'all were not always on whatsapp to begin with, so there's no reason y'all cannot leave.