Block video calls with Mikrotik
Solution 1:
The connection is already in the state table, and therefore it's not checked against the firewall rule list. That's what allows the existing connections to continue.
What you would have to do is drop connections from the state table, or reset all of them. I'm not sure how this works on Mikrotik, a quick google yielded the following:
:foreach i in=[/ip firewall connection find] do={/ip firewall connection remove $i}