First, some clarifications might be helpful. I'm assuming this is an indie provider and not an agency. Is that correct? And what exactly do you mean by blacklist? Would that mean a "no appt" policy for that specific provider or something more? Also, is your ultimate goal simply to see that provider again or something else? Depending on the answers to the above, one possible strategy could be to find a way to contact the provider directly, if at all possible. Maybe some research might turn up a number or email that might work. In conjunction with that you might need to use a different number and email than you have previously. But, in the final analysis, that's a lot of work and my personal way of handling it would be to chalk it up to "sh*t happens in the hobby" and move on to someone else. Life is too damn short to deal with unnecessary drama and there are plenty of fish in the sea.

and even back when you could review a US provider you still had to actually meet her in person in order to write a TER review.  

 
I would not worry too much about the threatened black list by the provider, the worst thing she is likely to do is put you on her own DNS list and after the treatment you received I can't imagine you want to use her again anyhow.

 
Expect for simply moving on to the next girl on your list I don't really see any recourse under current TER rules. Once upon a time you could post this right here on your local regional board and "name names" but because of FOSTA/SESTA that is no longer an option. The only thing I can think of that you "might" do is to find a way to contact the provider directly and share your experience with her. That could of course prove to be impossible, and I doubt you want to make a career out of trying to "punish" the assistant over this. My advice is to just move on to the next girl. Life is too short to hold grudges over relatively minor slights.

why I do my own screening, schedule my own appts and arrange all my meetings. Sorry that happened to you

Maybe finding other means to contact the provider outside of what you've already tried I don't know.
I want to assume the assistant doesn't have control of everything.
This really sucks and unfortunately is not the first time I have heard of a provider's assistant trying to sabotage them.
Lots of luck :/.

Did you send the assistant an explanation? And are you sure the provider doesn't agree? My assistant handles my emails but I can still see everything. It's my email account.

Problem Solved; Thanks for great comments

I wanted to update my original post. Asst contacted me and fully admitted her mistake. I was not going to see the provider at all, but she added more time to my appt w/o charge to make up for the mishap.  I was extremely hesitant but decided to give it another go.  My appt was awesome.

Having patience, not flaming on folks if they make a mistake and keeping positive is rewarded in this  business.  

So if you find yourself like I was, mad at an asst or provider, dont be a jerk or let anger get the best of you.  Wait a day or so to think clearly. Add a post to forum like this so you can get sage advice, comments  and support from the community.  They will not let you down.  And then act level headed in a responsible manner. The community will take care of you if you act appropriately and professionally

 And yes I have a second appt scheduled! (I did say she was awesome!)  

Thanks to all who added comments to this post. It helped.

I first tried to contact (PM) a local provider on another ad site P4, but got no response. Then a day later I sent an email requesting an appt and stated that I had asked for an appt on the other site (so verification would kick in). Another day goes by and I finally get a response from an assistant, saying the day I wanted was not available but the next week was. so I emailed back asking for that day. I heard nothing for days. The day before my expected appointment, I get an email telling me where the location is and for me to send a text upon arrival. I drive an hour in rushhour traffic and park at hotel 15 mins early. I send a text and get no response. At my appt time, I send another text. No immediate response. 10 mins after my appt. I get a text saying my appt is cancelled.  I try to stay calm and text back why I was not given more notice. At 15 mins late I get a text saying, sorry for the confusion, I can go up to room now.  Patience paid off. But the assistant must have been real busy or something to get things so mixed up, as well as really slow in replying.

I once booked with a rather famous provider who had been profiled in Playboy. While I was waiting for final instructions outside her hotel I saw her leaving with someone else only to get the silent treatment. I was pretty steamed but what happened next more than made up for it. She contacted me the next day with an apology and offered me 2 hours free of charge. It turned out we had friends in common and even phoned our mutual friend during the session. It was an incredible session  that I couldn't even review since I hadn't contributed. Alas she is based in Vegas so I haven't had an opportunity to see her again.