For what it's worth my former sibling tried a stunt similar ( note former he's been disowned)
Demanding to "talk" to my doctors, to give them his diagnosis etc etc..

After a couple of years somehow he figured out who I was seeing and rang them up ,he found out things he didn't want to know .

Such as they already new his diagnosis as I told them,they could not and would not accept his diagnosis , he doesnt have a high school diploma let alone an M.D ,it would be illegal for them to break confidentiality , therefore they would not acknowledge if they saw me or why.

Then to add icing on the cake , they suggested from his actions and behaviour he may be having a mental health crisis and there is help out there in his area .

They would not hear him out .

Now if your people heard your dad out , the following circumstances probably existed.

1.you live together , so he has an independent prospèctive about your past or current behaviour when not in session.

2. You may be under the "age of maturity"

3. He is still parent or guardian

The minute any or all of the above don't apply, them talking to him ,has to be with your written permission if at all , they cant afford to violate a patients trust or violate ethics or HIPPA laws.

Your dad sounds like he violated YOUR trust , that's a big issue that you will have to process ,but please do it from a place of peace and accepting it happened !anger will cloud both your judgement and message to him , focus your efforts at explaining "healthy boundries" and that Your therapy is for you ,not for him to "play old family tapes" or to sabotage your progress .