Good - that means port 53 is free now.
Restarting your Pi-hole container with the correct port mappings for 53 UDP and TCP should have worked then, and obviously, it did. 
You have to configure your network to make use of Pi-hole, see Post-Install - Pi-hole documentation.
You can verify if blocking is operational by running the following commands from a client that's using Pi-hole for DNS:
nslookup pi.hole
nslookup flurry.com
The latter should result in a 0.0.0.0 reply.
System load is reported as is via the underlying OS.
If you run Pi-hole in a virtualised environment, the reported details may not be accurate, see also e.g. High Load in docker on Synology.