I'm sorry to hear you had a bad experience, but it sounds like there was more going on in this practice than you were aware of at the time...and that your firing had nothing to do with your work performance and everything to do with a deceitful physician. They are out there, and coders get caught in the crossfire all the time.
The good news is that you obtained a very valuable learning experience, in fact, probably more than you know. Although it smarts to be let go from a job, you emerged with your integrity intact. If you had caved in and played the fraud game, you would have lost more than a paycheck. Kudos to you.
One of the most valuable lessons I learned when interviewing for a job is to ask about the current staff and business situation. I learned this the hard way.....I once replaced an office manager who was 'backing away from responsiblities'....when really "she won't do what we want her to do, so she's quitting". It wasn't long before I figured out that they were looking for another newbie to manipulate, and I skittered out of there fast!
Many years ago, I unwittingly took a job where the practice partnership was being dissolved: That's code for "the sh!t is about to hit the fan", and I found myself in the middle of a big personal and legal struggle between the two principals. That was the first episode in a long line of poor business decisions made by the eventual owner of the practice, and although it was stressful, I did learn a great deal about what not to do and how to handle adversity on the job.
There are little clues that can help you figure out if you're walking into a snake pit. If your interviewer doesn't speak well of the current employees....run fast! If you're replacing someone whose departure seems a little bit strange, then you might want to see if you can get the skinny on that. See if you can interview with other staff members, or if you know anyone that you might be able to call and speak to off the record. Any mention of legal troubles is a big red flag, as is any discussion that alludes to non-compliance. You absolutely have the right to ask if there is a compliance plan in place, and how they handle employees who don't code/bill according to guidelines.
Hopefully, you'll find something soon, and if anyone asks why you left the last job, be honest. You were asked to do things that you know were unethical, and it went against your morals and values. A good employer will recognize that as an attribute and be happy to have you join their team.
Good luck.