It is important to understand that iOS is a fairly closed operational system and ad blocking functionality beyond Safari is severely limited. The first thing you need to do is to enable DNS protection and choose AdGuard DNS server: AdGuard Settings → DNS protection → Toggle the switch to ON → DNS server → AdGuard DNS.
If it didn't help, do the following:
Open the same website in Safari. Since Apple allows content blocking only in Safari, we can block ads way more efficiently in this browser.
Or please do contact firstname.lastname@example.org
, we will provide you with further instructions on what can be done.