I think my father's doctor did something wrong medically to harm him. How do I get another doctor to see him?

my dad was admitted in the hospital with pneumonia, he was also having problems with some blood showing up in his catheter. I ask the his primary doctor to have a urologist to take a look at it before he was released from the hospital. After a couple of days the urologist showed up without examining my dad changed his catheter from a size 16fr to a 24fr...now my dad has bleeding none stop has to go to the hospital every 2 weeks for a blood transfusion. The doctor said it's nothing he did...that my dad has a recurring prostate cancer with damage to his bladder from radiation seed implants. Now I cannot get an appointment with another urologist because of his previous problem at the hospital and his age(84 yrs old). I think it's because of who the doctor is and the alliance between this group of doctors in this clinic. No other doctor is willing to examine my dad and give us the correct diagnose.