It's been a while since I worked in PhD/research admissions but if I am honest, this does not strike me as an unsual scenario. Frustrating, absolutely, but not out of the ordinary.
Typically you'd engage with an academic, find out if they wanted to supervise you, narrow down your proposal and then agree to submit a formal application. An academic isn't there to assess your previous grades, beyond potentially giving some advice about what may or may not be possible based on previous experience.
A central admissions team then looks at your app, spots that you don't meet the minimum requirements, then contacts the academic department to establish whether they want to make an exception. There are a lot of moving parts as to whether that does eventually happen, and it's not unsual for the outcome to be 'no'.
I can only repeat what I said in a previous thread, they're not going to waste their own time going back and forth if they genuinely have no interest or there was no possibility at all given your background. The one thing academics don't have is spare time to string people along. I don't think you were deceived although the outcome clearly is a disappointing one.