The New Zealand Herald received detailed data usage logs from one customer in Dunedin and another in New Plymouth which show over-counting by up to 139%. Both have raised the matter with Telecom, but have yet to get an explanation.
Over-counting of data usage could lead to extra charges and throttling of customers' internet connection speeds.
"We showed Telecom five days of data as early as February 14," director Mark Peisker, of Dunedin's CueClub, an internet lounge and pool room, said.
"There was massive variance between our data and that reported by Telecom. I said to them: `Your counting has very little to do with what comes down my line to me."'
CueClub's data taken from its two internet routers shows an average of 62% over-counting during a three-month period, the worst month being May, when Telecom counted an extra 118.24 gigabytes (GB) of usage, amounting to $203.97 in overcharging.
Alister Lambert, in New Plymouth, first logged a fault with Telecom in January, and readings from the past four months reveal over-counting of about 30% each month.
Mr Peisker and Mr Lambert have been told Alcatel-Lucent, which runs Telecom's networks, found its checks accurate.
Telecom spokeswoman Emma-Kate Greer said despite working closely with Mr Peisker and Mr Lambert for many months, Telecom had yet to find a definitive answer.
"We are determined to get to the bottom of what is causing this and where the issue lies," she said, adding that in the meantime the company was removing their caps for data use.
"We monitor the network and billing files very closely and stand by the integrity of our metering system," she said.
"We have more than half a million broadband customers for whom this system works smoothly."
The difficulty in knowing how widespread the problem might be in New Zealand was that few customers would know how to check their usage.
Telecommunications Users Association chief executive Paul Brislen said he had seen posts on internet forums indicating other internet providers also had counting problems.
"There is no independent authority or independent assessment of these meters, so there is really no way of knowing for sure whether the 60GB of data you've used has actually been used." He said there should be third-party oversight to check accurate metering.
Telecommunication Dispute Resolution manager Derek Pullen said the service had received several complaints regarding metering. He said the service had identified this as a systemic issue, and would shortly be raising this with its members.
A further complication is that while most users in New Zealand will have a monthly data cap on their internet usage, what happens when it is exceeded varies.
Plans such as Mr Lambert's are throttled back to dial-up speed when the data cap is exceeded. Mr Lambert noted when that occurred there was no discrepancy between his download figures and Telecom's.
Other plans like CueClub's charge per gigabyte in excess of the monthly data cap; in their case at $1.50 plus GST per gigabyte. Depending on their base plan, others would be charged $2 to $4.44 plus GST per extra gigabyte used.
