Never heard of fistula and or resection for ibs.
Understand fully your frustration as I was diagnosed with ibs for 30 years till a number of emergency intakes to hospital & they identified crohns initially within 30.seconds of my barium scan that was confirmed by all the other tests, bloods, colonoscopy, ct scans etc..
You know your body, gently but firmly & politely keep stating your case.
Staying in my prayers.
Shalom my friend, john