BigPond services were unavailable over the weekend as Telstra migrated customers to a new billing system.
Customers were notified that: "Access to (an) account management feature has been temporarily suspended. Your BigPond account is in the process of being moved to a new, improved billing system."
According to a BigPond spokesperson, some 60,000 Sydney-based customers were migrated to the new billing system over this weekend and all affected customers should have received an e-mail from BigPond outlining the move 30 days ago.
Telstra is in the process of an overhaul - estimated to be worth $500 million - of its entire billing system.
It is critical for Telstra to get its billing systems in order after years of customer complaints about inaccurate bills that led to questions being raised in Parliament during Senate Estimate Committee hearings.