Commanders, might be a stupid or misplaced question , but have you tried to configure Google's DNS servers, instead of default ones (which are most probably given by the ISPs)? Might be worth a try, if not tested. I have issues with some MMO games if I use my ISP's DNS so could be a similar issue.
Just configure your network settings to use the IP addresses 8.8.8.8 and 8.8.4.4 as your DNS servers and give it a go-if it doesn't work you can wipe the changes out.
Also quite helpful could be if you can download wireshark (freeware) and start to sniff with it on the correct network interface, prior attempting to connect to Frontier. ED support will easily spot the problem in the captures later-server unreachable, timeout, wrong address, no port forwarding, etc.. I think network troubleshooting without wireshark pcap traces is just guessing in the dark
As I said, apologies if those are misplaced or already discussed & tested..hope they could help somehow
Cheers!