Premium account, had this problem like 2 weeks ago, stuck on Connecting and Unable to Connect for just Warmane servers. Internet, other games, Discord, everything runs perfectly fine. I tried Vanilla and it works fine, TBC and WOTLK Warmane servers won't let me log on all of a sudden. Like for the last 2 hours this has happened and I was just on fine playing like 3.5 hours ago. This happened 2 weeks ago and then the problem dissipated and now all of a sudden it's back. Any help is appreciated thanks.
You can try the basic things like move Cache and WTF folder somewhere on desktop for example and see if that helps for your game and in case it doesn't, you can move them back to wow folder. Let me know how that works for you and we can see the issue further.