@Michel370 You are absolutely right, no way should you assume that the booking will be honored and just show up. No communication from host and the listing being taken down means it is pretty well assured that this booking is a no-go. You need to contact airbnb, which I realize you have been unsuccessful at so far, but, as @Emiel1 says, try phoning, or contacting through Twitter, which people report get quick responses. Phone numbers are pinned to the top of the first page of the Help forum here.
You should not lose 50% of the booking if the listing is no longer active, you should be entitled to full refund.