If anyone got problem with reaching bitcoin-rpc server located on vps, the best way in my opinion would be port redirecting over shh. By this command:
ssh [user]@[host] -p [port] -L 18332:127.0.0.1:18332
You will be able to send comands to testnet rpc-server via your computer terminal as localhost.
Please keep in mind that exposing your node's RPC interface to the entire internet is considered to be unsafe. RPCs are not encrypted so anything that you send to your node will be in cleartext for any man in the middle to see. This includes things such as your RPC username, RPC password, and wallet password. If an attacker were to see any of this ...