I'm sorry you're going through this. You're facing two different (but related) problems: getting the fistula found (and treated), and figuring out your problem defecating. As far as the fistula goes, what has your doctor said? Have they considered a referral to a more experienced doctor, or a different technology, or have they just given up? As far as the toilet trouble goes, perhaps the abscess is obstructing things, or perhaps you've developed a prolapse. Normally a defecogram can help identify what's getting in the way.  Again. What has your doctor recommended or said?

It's completely understandable that if your doctors aren't offering you a constructive plan that you're considering abandoning your pouch. Hopefully you can get them to make some intelligent recommendations. Good luck!