Hi Emily, 

so sorry to hear about your dad's diagnosis. I know it can sometimes be frustrating when you cannot get a straight answer from the doctors and you leave more confused than when you turned up. My partner's Mum had lots of visits to and from different doctors and hospitals in the early stages of her diagnosis. The main thing to remember is, even though you are angry, you shouldn't be focusing on who may be responsible if things have gotten worse. Doctors and Nurses do try their hardest to give the best care but unfortunately are very short staffed a lot of the time. The main thing I would suggest is for you, your father and anyone else who has concerns to write them all down to bring up on his next appointment. Then make sure you also take notes on what information they give you so you can all go home and read through it together. It's sometimes a good idea for someone else to go to the appointment, someone that isn't family but someone you can all trust as they will be less emotional and may pick up on things that you haven't. The more ears, the better. 
I know it's easy to be angry but just be there for your Dad and make sure you are all prepped for his next appointment and make it known that the whole process has been very confusing for you all. They will do their very best to make things clearer for you. 

All the best to you and your family x