To check/monitor usage of each Windows VPS, we have installed bandwidth meter tool on our main HyperV node. This tool will measure bandwidth of each VPS as a whole. You can submit the ticket from client area to avail necessary login information to check bandwidth usage of your VPS. To monitor bandwidth usage of each service individually, you will need to install third party bandwidth monitoring tools in your VPS.
To monitor bandwidth usage in Linux VPS machine, you can install following command line monitoring tools. These commands are very useful to monitor network and find bandwidth bottlenecks.