I downloaded Blokada from AppStore and also checked with its repository to check BlackList.
I enabled some advanced features and manually block some URL from Activity tab. But after add url to blacklist, safari always allow that URL and will give response everytime.
I am using Iphone 7 plus with 14.3 OS.
The same thing happend with Wifi connection and mobile network.
Give it at least 10 seconds and then hit refresh in Safari. Possibly swipe close safari and power cycle Blokada if it still doesn’t work. There may be some entries stuck in cache and a small startup delay before the filter has re-initalized after your changes.