Looking for a working example of USSD session for SIM808

Hi all,

I'm looking for a working example for a code based USSD session for SIM808.
i.e. I send the unit an SMS. Once the SMS is received, I want the unit to look up the account balance via USSD and report back the balance via SMS.

I am using the DFRobot_SIM808 library on Github, but have been unable to find any examples I can work with.
(https://github.com/DFRobot/DFRobot_SIM808)

Anyone able to assist?

Thanks in advance.

Matt