The contracts of the BM and SM need to be reviewed and alternative service providers found. It would be advisable to take legal advice from a good quality experienced strata lawyers .
It sounds like you also need by laws against the dumping and allocating costs of removal to the owner of the lot. It shouldn’t be necessary but this is the way that OC govern their own buildings.
For all this, take legal advice so you have the right strategy and it all clearly dealt within the strata law framework and you can achieve your goal. It will take time to resolve. In many cases people dump because they sees others doing it and don’t really know what else to do – so combined governance with information about where to take unwanted items, or a ‘take your junk’ service so people know they can in fact get their rubbish removed
Finally, most people are apathetic until they understand they are paying for something in their levies which is not their cost. This is an individual responsibility and individual cost.
The Local Council should be made aware of the problem, as it is possibly a public health issue. Be aware however that many Local Councils will be happy that dumping and disposal is being handled by the OC. In fact, there is so much illegal dumping by tenants in some LGAs (esp.Waverly) this may be seen as a solution to their problem. From memory at one point, that council explored the option of passing the cost to OC and the OC to pass to the occupier/host. That is not a path you should go down.
Cheers