apt-get stuck on "Waiting for headers"

As others have mentioned, the problem is the network (teksavvy/rogers). Seems they're blocking the User-Agent that apt-get uses by default. I wiresharked the requests, and was getting a slew of TCP retransmissions. To fix the problem, change the apt-get user-agent, by adding the following to /etc/apt/apt.conf.d/99user-agent

Acquire
{
  http::User-Agent "Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/70.0.3538.110 Safari/537.36";
};

This is from https://dmfrsecurity.com/2018/12/10/changing-apts-user-agent-string