Ethernet doesn't work in proxy environment

I'm trying to set up Ethernet on a university pc with Ubuntu 16.04. There are university wide proxy, and I connected 2 other windows PC's to it using .reg file, proxy adress, port and login, password, which I was provided by the university. I tried setting proxy adress and port, using gui (as I did for windows) but it's just doesn't work. Firefox says "Unable to find the proxy server" or sometimes "we're having trouble finding that site" and ping 8.8.8.8 says "Network is unreachable" ping google.com says "unknown host".

says:

enp6s0    Link encap:Ethernet  HWaddr 1c:6f:65:91:3e:4a     
          UP BROADCAST RUNNING MULTICAST  MTU:1500  Metric:1   
          RX packets:13462119 errors:0 dropped:16 overruns:0 frame:0   
          TX packets:351453 errors:0 dropped:0 overruns:0 carrier:0   
          collisions:0 txqueuelen:1000    
          RX bytes:893149471 (893.1 MB)  TX bytes:71061986 (71.0 MB)   
   
lo        Link encap:Local Loopback     
          inet addr:127.0.0.1  Mask:255.0.0.0   
          inet6 addr: ::1/128 Scope:Host   
          UP LOOPBACK RUNNING  MTU:65536  Metric:1   
          RX packets:6683368 errors:0 dropped:0 overruns:0 frame:0   
          TX packets:6683368 errors:0 dropped:0 overruns:0 carrier:0   
          collisions:0 txqueuelen:1000    
          RX bytes:494614018 (494.6 MB)  TX bytes:494614018 (494.6 MB)

All 3 PC's are connected to the same lan hub and I tried to switch ports and cables around and nothing changed, on windows internet works and on linux it doesn't. Also, for some reason connection just turnes off every couple minutes or so. Lan cable 100% works. first time Linux user, any help would be of great use. .reg file contains: [HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Internet Settings] "AutoDetect"=dword:00000000 "MigrateProxy"=dword:00000001 "ProxyEnable"=dword:00000001 "ProxyServer"="my_proxy_ip:3128" "ProxyOverride"="some sites" (redacted proxy ip and override just in case)