@616471991zlm If you already have an existing modem that would work with the service then I don't see any issues about it, though it is always best to use TPG issued modems. Our customer service team would help.
BTW all TPG NBN plans come with a free modem.
We understand that you'd like to keep your service with TPG and we are happy to inform your that the account cancellation has been withdrawn, @616471991zlm.
As mentioned via PM, your account is still paid.
To avoid service disruption, please settle a new renewal for the next billing cycle.
These articles can guide you on how to use your TPG My Account:
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Let us know should you need further assistance.