Here is some information about the Aircover policy: https://www.airbnb.co.uk/help/article/3218
As you can see, timing is quite important. So, at what point did you contact the host about the issue and what did the host say? Was there any attempt to fix the WiFi? At what point did you contact Airbnb?
How long did you stay? Did you get refunded for the two weeks you didn't stay, but wanted 50% back on the nights you did stay? Or, are you saying you only got $3 after asking for 50% of the total booking?
Do previous guests mention WiFi issues in the reviews?
RE your review, when did you leave it and did you see it, i.e. was it published already? As already mentioned, the review will not be posted until after the 14 day review period is over, or if the host leaves you are review too. So, if the host doesn't review you, you have to wait until 14 days after check out to see your review on the listing.
However, if the review as already published and then removed, it is possible it was due to the mention of 'fraud'. I have heard that reviews that mention resolution cases can be removed. Also, as you requested and was denied a refund, the host could ask for the review to be removed because it's retaliatory. It's then at Airbnb's discretion whether they remove it or not, but they don't remove reviews that often.