Annoying delay while using skills
If it was a server issue, everyone would have the issue. It sounds like there is a problem between your modem and anet’s servers. Your ISP should have actually sat down and asked for the IP, and told you to pingplot from your modem to that ip on the server you are having the issues with. That will start by actually proving that it really is the anet servers (mind you, I would say most of the time, it actually shows it’s not and where the issue actually is).
Hi! NA or EU server? And when this happens, is it during world bosses/meta-events, when there’s a lot of people in the map? Also did you manage to try and trace the ip using programs like PingPlotter or WinMTR? If nothing else, these might let you know where the problem are.
Have a look at Anet’s FAQ. If you contact them, they’ll start by asking you to go through the steps outline there.
And yes, I agree with Ell that your ISP didn’t really do thorough troubleshooting with you. Even if your connection to your ISP is fine, their connection to Anet may be broke. You can diagnose it by plotting your ping, but only they can fix it by routing you via a different network. Or a VPN may work too.