Perhaps try some positive, friendly ways of either getting your money back, or moving your booking
first, before getting vindictive.
If and only if you are unsuccessful, your credit card company can often help.
If that is also unsuccessful, a bit of paperwork lodged with the magistrate's court in the state in which the flying school is located is the simplest method of legal action.
Procedures vary from state to state - I see you are in Melbourne, so I guess the school in question is also in Victoria.
PM me if you want some specific info.