UPDATE | Customers who are looking at moving to a different plan because of Telstra's billing foul-up may like to use Whirlpool's BroadbandChoice Plan Finder to find a better deal.

Telstra wrote to some QLD customers in October, admitting it had discovered a problem which had resulted in some usage not being charged to users' accounts (causing overall usage figures to be lower than they really were).

As a "measure of goodwill", Telstra said it would not charge customers for their additional usage that was not attributed to their usage meters.

But Telstra yesterday wrote to customers again, trying to push them on to more expensive plans by threatening to bill them for excess usage if they continued with their current usage patterns (which, for many users, would have seen a large jump in billed usage in October).

Despite reassurances in its earlier email that customers would not be penalised for Telstra's usage metering foulup, it wrote in its latest email: "If customers decide not to change to the 3GB plan and remain on the 1GB plan, they would be liable for 1GB of additional usage charges in October if they used 2GB during that month. This charge would appear in the bill received in November."

One Bigpond customer told Whirlpool his usage had been understated by 60%.

He said the Telstra foulup was very annoying. "I switched to a lower volume plan on the basis of (a) the lower apparent usage and (b) the repeated assurances of Telstra tech support that there were no problems with the usage meter."

He said he kept his own usage graphs which seemed to contradict Telstra's own usage meter, and after eight phone calls to Telstra technical support, he was told by "James" on August 29 that "UDP and upstream TCP traffic" was no longer being charged (clearly an incorrect statement given Telstra's later emails.)

OPINION | This chain of events illustrates why Telstra's usage metering model is so flawed. Telstra demands that customers trust its central metering system and refuses to recognise the validity of any metering done on a customer's own computer. Yet, when Telstra's metering system proves faulty (as it has on so many occasions), the customer has to wear the cost and inconvenience. It's also offensive that Telstra is trying to use the latest foul-up as a marketing opportunity to push customers onto more expensive plans.