The landlord has a responsibility to provide healthy and safe accommodation. Mould is a potential health hazard so they are required to fix this, regardless of who signs a lease for when.
The Owners Corporation (body corporate) has a responsibility to maintain and repair common property (like walls) and the landlord should be hassling them, not you.
If the building is less than six years old, the Owners Corp should be hassling the builder to fix the defects.
However, unfortunately you are the low man on the totem pole and everyone is shifting their responsibilities down to you. Firstly, you should be demanding a rent reduction from the time that the mould was first reported.
Secondly, if you are in the last week of the tenancy and you haven’t either been give a notice to quit or signed a new agreement, you are effectively in a periodic tenancy which means the landlord has to give you three months notice if they want you out.
The have to fix the mould, regardless of whether you sign a new lease and you should tell them that you will only sign a new lease when the mould is fixed.
Contact the Tenants Union and they will explain all your options and you will also find an invaluable fact sheet on mould there.