The Supreme Court has unlimited jurisdiction. There is no lower limit, though in many situations people do not start in the Supreme Court if they do not have too because of the costs.
The other side has elected to go to the Supreme Court, as is their right. Could be a tactic to frighten you to settle, or it may be they do not care about costs and see this is a matter of principle.
If the court registry accepts the case, it is accepted.
You may be able to argue in court later it should be heard by a lower court, but it is the judge's discretion.
We had a case recently in Vic where the other side went straight to the Victorian Supreme Court for a $50K claim. It happens.
Stop focusing on why they used the Supreme Court, get a lawyer quickly and either pay or contest. There is a time limit for filing your defense.