Blaming a "misalignment in the system", Robbie told Karen: "As far as we're aware, we're all good and moving forward."
But a month later, Karen opened her next bill and realised her bill was even more expensive.
Telstra had added her usual $400 onto the $465,000 it was trying to charge her.
"Their billing process failed, their technology failed, their customer service definitely failed and their management have failed," Karen told A Current Affair.
Telstra executive Michael Ackland eventually became involved, apologising "unreservedly" to Karen for the mistake.
"There were two issues — there was a system glitch error that created the original problem and then human error to not pick it up as quick as we possibly could," Mr Ackland said.
"(Karen) should ignore that bill because it takes a little bit of time for the billing systems to process the removal, and we have confirmed with her in writing that all those charges are removed and she should ignore them."
Tech expert Trevor Long said for a bill to cost that much, the family would have to watch 30,000 movies in the month.
"I think if there was actually that much traffic going through your home network … I don't think the average home router or home network could cope with it," Mr Long said.