I don't think ViaBTC restricts miners from using proxies.
Have you tried to connect your miner without the proxy? If it's connecting properly, meaning the proxy might be the issue, you need to change it to maybe HTTP proxies instead of using socks5 and proxies that encrypt data sent to the pool server.

Would you mind to share the unit model of your miner?
And the type of proxy you use(HTTP, Socks4, Socks5)?