Why doesn't it block the site by url?

Question

network hardware

There is a Promsvyaz zxv10 h208l modem at home.
Added 8 url sites to the list of blocked sites by url.
For the first few minutes, the blocking was carried out, i.e. connection from sites was dropped and there was no access to blocked sites. But after a few minutes I checked - the lock does not work. Blocking is carried out but only on one site - the first in the list.
Who knows how to solve this problem? I need to make it impossible to access sites on the black list. No way.
Thank you for your attention.
PS I searched for solutions on the Internet, on the forum - the search did not lead to anything.