Very bad experience...
Here is how you can NOT have the same bad experience:
1) Sign an NDA with them and DO NOT let them put their name as an inventor of your invention. Their JOB is to be a design house and not to steal your inventive idea. They were way out of integrity and good business practices on this element.
2) Ask for a VERY CLEAR Time and Materials billing system so they do not fabricate billing events with nothing to show.
3) Have your attorney draft a contract that explains the above.
The Owner HATES it when you ask for detailed billing documents and gets VERY ANGRY when you do.
My suggestion: Steer clear of them until they clean up their act. There are LOTS of legitimate design houses around.