I have been banned for asking to many questions on Physics Stack Exchange for 1 year. During this time I am not allowed to revise or update my published work. I have asked that my work be invisible with my ban unless I am allowed to refine my questions and answers. Are they legally allowed to display my Q & A and comments against my will?
Use of SE is subject to the terms and conditions specified here. Section 3 says "You agree that all Subscriber Content that You contribute to the Network is perpetually and irrevocably licensed to Stack Exchange under the Creative Commons Attribution Share Alike license." That means that your contributions can be used forever. That means the stuff is there, end of story. Section 11 on Termination says "Stack Exchange may also terminate, block, or suspend any and all Services and access to the Network immediately, without prior notice or liability, in its sole discretion, for any reason or no reason at all, including but not limited to any Subscriber breaches of any of the terms or conditions of this Agreement". That means you can be banned. So, yes, what they did is legal.
In addition to user6726's answer, which is right, please notice that since we license our contributions under Creative Commons Attribution Share Alike license anybody is free to copy, keep, publish or distribute our posts anywhere or even modify them with very few restrictions. Our will doesn't matter now because we gave permission when we licensed our work on clicking the "Post Your Answer" button.
And of course you have the right to post modified or improved versions of your posts anywhere else.