@Hannah849 As a host yourself, I am surprised that you didn't follow proper Airbnb procedure. When you arrived to find the place not ready for guests, indeed you should first notify the host, but why did you phone him? You should have used the Airbnb messaging system, so there was a record of the exchange.
When he indicated that he couldn't remedy the issue for you, you should then have immediately called Airbnb to cancel, stating why. Not just left it to the following day with a promise from the host to refund. Had you followed proper protocol, you probably would have been issued a refund by Airbnb, no problem.
At this point, having not followed the correct steps, I guess you are just going to have to keep dialoging with Airbnb to see what can be done. If the reservation hasn't been cancelled, you aren't due a refund. It is still an active reservation, and as such, you have the right to stay there, but I can't imagine why you would want to.
What were you thinking, IBing and showing up 15 minutes later? How would a host have time to prepare for a booking that quickly? Why would you do that without bothering to communicate with the host to make sure he could accommodate you that quickly?
I'm really quite bamboozled that someone who is a host herself would act like she was booking a hotel room with 24 hour reception and maids around all the time.