Example or abusing alt- having alt account in other group and plundering it for free coupons.

You can play on few accounts as long as your main one doesn't benefit from alts.

There are situations like lack of activity in group, when using alts might be only way to join GNW and so- and from what I've been told, using them like this is ok.

This is something you should ask customer service via ticket system, not on forum.

You can find it under the question mark on game window:

Also by opening "My Center" on website of game and there's "My Customer Service" tab.

You c*so try to contact them via official game discord or by sending private msg to mods from customer service/bug section of forum.