So, you've been screwed with in several levels, and I think that there's very little chance you get any payback. It happens. Put it in the lessons learned column and move on.

More precisely, move on to looking for a new job. If you have been very productive and have had lots of responsibility, that can go a long way to improve your resume. Update it, and start hunting. As someone else suggested, "Drop productivity, but no engagement", and use the extra time to job search.

One particular tip: if they put such ridiculous terms in the contract, you should probably do all job searching in your own hardware (phone, computer). Just in case.