Not quite the issue here.

You absolutely have the right to free speech in the US. But any owner of private property can pretty much ban you from that property, for example (there are certainly some protected exceptions, but in general 'the law' is on their side).

Similarly, Rackspace has the right to stop servicing their customer if they feel the customer has violated the contract. Now, whether or not a court has to step in to determine the validity of the contract, etc, is a completely separate issue.

But this most certainly all has absolutely nothing to do with constitutionally protected speech.