How are you? I'm sorry to hear what you have been through for the last 20 years. Surgery is almost always necessary to cure an anal fistula but some complications can occur including infection, anal fissure, recurring abscess or scarring. If the surgery was not successful, it is best that you discuss this with your doctor or have a referral or seek another specialist's opinion for proper management. Further evaluation may need to be done. Take care and do keep us posted.
May I know how is your anal fistula? Did you find a way to manage it?