20 bomb

That's understandable, though it would likely be too much to keep track of what every player has used in every game in such a way to track that properly. Especially considering that your teammates can do damage to enemies and you can get credited for a kill.

There are lots of factors to be considered. It does suck that it's not possible to get it in pubs, especially for this period of time it's been out, though that's sadly how it is.

It’s was in pubs but i never used a relic weapon which is stupid that i can’t get it 

Was this in pubs? Keep in mind that kill & damage badges are disabled in pubs due to the relic weapons, as they make it easier to get these badges.

You can still get them from ranked, just not from pubs.