Welcome to the Community!
We're glad that your NBN service is already installed and working. If you didn't request to have your Telstra phone number ported to TPG, then you can now contact them and cancel your account to avoid being billed further.
As for your Bigpond email addresses, they will stop working eventually once you cancel your Testra account. I would suggest that you check with Telstra and clarify if there's a specific time frame that you can use them before they cease to work.
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