I said "be a demon" on lfg and was banned, was this really nessecary?

Yes as lfg is meant as looking for group not posting jokes emojis etc

My account is suspended I think I put in a review but I did nothing and said nothing It said something about soliciting and I def have never ever done anything like this

Did you, by any chance, use the Looking For Groups (LFG) to either try and sell or buy in-game goods? That would be classed as solicitation in this instance and would explain the ban as it's against the LFG rules.

I only posted in an lfg private group to TRADE exact word we’re looking to trade my demon crazy guy and old man masks.

80%+ of the posts on the LFG are exactly what I did and they never get banned? It’s exactly what that LFG is used for most of the time

And if they get reported then they'll receive a suspension as well.

As ngocphi has said,LFG posts are for finding people to play with & that's it.Trading of any kind,even for in game currency,is not allowed.

Go take a look at the rocket league lfg page. 99% of it is looking for trades. Also my ban said that I included inappropriate words but I didn’t.

Yes, trading in the game is allowed, but LFG posts are not in the game. You can only use in-game mechanics to trade.

Which is all that I did

Not according to your own words:

"I only posted in an lfg private group to TRADE exact word we’re looking to trade my demon crazy guy and old man masks."

LFG is literally only for looking for other players to play with. Literally anything else (trading, selling etc) is not allowed on LFG posts.

You can trade in game but anything posted on LFG regarding anything except looking for others to play with can result in a suspension.