I met a similar problem.But the error report is about
[SSL: TLSV1_ALERT_ACCESS_DENIED] tlsv1 alert access denied (_ssl.c:777)
First I tried this https://python-forum.io/Thread-All-pip-install-attempts-are-met-with-SSL-error#pid_28035 ,but seems it couldn't solve my problems,and still repeat the same issue.
And Second if you are working on a business computer,generally it may exist a web content filter(but I can access https://pypi.python.org through browser directly).And solve this issue by adding a proxy server.
For windows,open the Internet properties
through IE or Chrome or whatsoever ,then set valid proxy address and port,and this way solve my problems
Or just adding the option pip --proxy [proxy-address]:port install mitmproxy
.But you always need to add this option while installing by pypi
The above two solution is alternative for you demand.