Welcome to TPG Community!
TPG does not have an invoice system or BPay facilities for the monthly fees. We only accept credit card and direct debit payments for the monthly automatic debit.
I recommend having a read of the following TPG Community articles below which will guide you on how to access and check your billing info online via My Account:
Your billing cycle and advance payments explained: https://community.tpg.com.au/t5/Accounts-and-Billing/Your-billing-cycle-and-advance-payments-explain...
TPG My Account - Accessing your account information online: https://community.tpg.com.au/t5/Accounts-and-Billing/TPG-My-Account-Accessing-your-account-informati...
Updating your payment details online: https://community.tpg.com.au/t5/Broadband-Internet/Updating-your-payment-details-online/m-p/17164
Please check it out and let me know should you need further contact for assistance.