robots.txt seems like it should be a legally-binding terms of service which would make them outright copyright infringing.
Sue for $180,000 per infringement which should be calculated for each illegal API call.
Was your robots txt written by a lawyer? Does it hold up in the court?
They copy books illegally by scanning the pages and try to hide the whole thing under 3rd party companies. They care 0 about the law. I suspect I know why now.