Buyer’s remorse - simply changed your mind, found it cheaper somewhere else.
Delays with the NBN connection and decided to change providers. As the service provider does not have control over the installation schedules by NBN, they cannot offer a refund for the cost of the modem. As the modems are not locked, you may use it with other service providers.
Decided to get another model and would like to swap the first modem purchased. Modem swap to another model is not allowed unless the modem has not dispatched yet and has not been sent out yet. If you would like to get the other modem with another model, you may need to make a new purchase and you will end up having 2 modems.