Welcome to TPG Community!
I was able to pull up your account using your Community details and carefully checked what the charge is for.
Since you switched your account from ADSL to NBN, we have deducted the unused portion which is $32.90 from your previous cycle which was paid until 12 April 2019.
Since your NBN service got activated yesterday, 26 March 2019, a new cycle has started. Instead of paying $69.99, the $37.09 will now cover the period from 26 March 2019 up to 25 April 2019.
You may check all these information by logging in to 'My Account
The link below will provide you with more details on how to utilise 'My Account':
Please don't hesitate to let us know should you have further queries.