Handle proxy error

How i can handle proxy error like
`proxy error: "HTTP/1.1 503 Service Unavailable\r\nServer: squid/3.3.8\r\nMime-Version: 1.0\r\nDate: Mon, 05 Mar 2018 17:01:39 GMT\r\nContent-Type: text/html\r\nContent-Length: 3280\r\nX-Squid-Error: ERR_DNS_FAIL 0\r\nVary: Accept-Language\r\nContent-Langu`

i have this code
```
case HTTPoison.get(url, headers, request_options) do
{:ok, response} ->
IO.inspect(response)
{:error, %HTTPoison.Error{reason: reason}} ->
IO.inspect(reason)
{:error, error} ->
IO.inspect(error)
_ ->
IO.inspect("Another error")
end
```