Hi @Gayathri1414 and welcome to the forum.
The real estate industry is not known for being on top of the integrity ladder at the best of times although is usually well above the pollies.
I’ll assume the spa was portable, eg not built in like an in-ground pool or tub. Unless there was a written inventory of portable appliances and equipment included, it could become a ‘he said-she said’ as to whether it was included, but I understand your chagrin that regardless if there was misrepresentation or misunderstanding (even by the estate agent) that while not responding is bad form it is not anything that will result in a censure or ‘please explain’ notice without that aforementioned inventory.
Some reality is that making formal complaints makes us feel better but is also the case that when our complaints are ignored or fobbed off it raises our ire further by revealing how powerless we are as individuals where there is no clear legal issue in play.
If you are going to make a formal complaint be sure to include exactly what you want as an outcome, and be prepared for anything from ‘thank you for telling us’, crickets, an apology, or a spa. Using the ACCC complaints template could be helpful.
The Real Estate Institute of Australia has links to each state organisation as well as to state tribunals. Note these ‘Institutes’ are not ‘services for consumers’, they are ‘trade organisations’ and can be counted on to act accordingly.
Your state tribunal might be the best agency to contact if you desire to make a claim for the cost of the ‘missing’ spa rather than only make a complaint.
If you proceed please let us know how you go as it could be helpful for others who may find themselves in a similar situation.