Welcome to the community!
TPG is a prepaid service, which means we charge a monthly fee in advance. And as part of our billing system’s automation, we charge 7 days before the next billing cycle to make sure that account will not expire. It is normal for the 2nd payment dated 27th of March.
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...
Let us know should you require further assistance.