This isn't the limitation of free speech, this is a private company telling one of its users that they aren't welcome due to their behavior. It's like if you were at a store and started soapboxing about <insert alt right conspiracy bullshit here> loudly right in front of the register, the manager of the store is 100% allowed to ask you to leave. Freedom of speech means your speech isn't illegal, not that you will suffer no consequences for it.

ETA: some people made some comments below this that made me want to clarify a few things:

1) Twitter being publicly traded does not automatically make them beholden to every person on Earth, especially in matters of free speech. They're still allowed governing their platform in whatever way they see fit.

2) a better analogy might be a comedy club on open mic nigh.t. If you get up on stage and start making racist, sexist, homophobic, etc. Jokes the club owner has every right to throw you out. Yes, it's a public forum, but limiting your use of what is ultimately a private (i.e. not government owned) establishment does not constitute a violation of your rights unless it can be proven that you were denied access due to your membership in a protected class, or based on your gender, etc. Free speech doesn't protect you from (peaceful and appropriate) backlash.