have a read of this
I am not having issues in australia
try going lower and using telnet as a test (this will let you know if its a network or protocol HTTPS issue)
also try in your browser as well
do a trace route from your internal systems to letsencrypt (if this stop at an internal IP then you know it's something there)
Please note: akamai ips will be different for you
In summary one of 3 issues
A) DNS is not working as it should be flush your DNS records if you have used LetsEncrypt before
B) You firewalls are blocking port 443 going out (unlikely but it could be an issue) - tracert would confirm that
C) You firewall is blocking json responses (unusual but could be)
Andrei