How to set up a normal server robot with an IPV6 proxy?

Question

proxy

Hello dear.
The other day we took a virtual server + IPV6 subnet from one hoster. The hoster set up proxying for us.
We got a proxy list like:
"IP address: port: password: login"
And at the output of each such connection we have a unique IPV6.
Everything worked fine until there were 10-20 proxies in operation at the same time.
As soon as I increased this number to 150-200, the proxies began to lag terribly, namely, instead of the required 3-4 actions per minute, only 0.5-1 actions were performed.
The hoster says everything is fine on their side, there are no loads, everything is fine in the logs too.

I had this idea that the problem could be that:
A) either my windows does not allow 100+ connections to one server,
or
B) the server does not allow 100+ connections from one computer or IP address

The hoster is silent and blames everything on us, on software, etc.
Tomorrow I will look for a freelancer-administrator to help set everything up.
But now I would like to read your thoughts.
Thanks, I'm waiting for your reply.

Answer 1

OS Centos 6,
proxy via Squid Version 3.1.23