Complaints to the telco ombudsman have hit their lowest level in six years, indicating investments in mobile infrastructure could be paying dividends.

Complaints about telcos have hit their lowest level in six years, but the industry Ombudsman continues to receive an average of about 360 a day.

Consumers lodged 33,351 complaints to the Telecommunications Industry Ombudsman (TIO) between October and December, figures released on Thursday show.

That’s down 6.7 per cent on the previous quarter and 12.9 per cent on the same time in 2012, making it the leanest quarter since 2008.

“It is a positive story for an industry that has very publicly committed to doing better by its customers, and has invested substantially in mobile network infrastructure,” said Ombudsman Simon Cohen.

He pointed to a big drop in complaints relating to mobile phone coverage, which halved between April and December to reach their lowest level since mid-2010: about 30 a day.

Overall, the Ombudsman received about 200 new complaints regarding mobile services a day, down 4.9 per cent on the previous quarter.

Complaints about drop-outs and slow data speeds dropped compared to the previous quarter, but several other types of complaints increased.

About 20 per cent more people complained about poor information in their mobile phone contract, while complaints about excess data charges spiked 13 per cent.

Mark Callender from the Australian Communications Consumer Action Network said his organisation was particularly concerned about the increase in excess data complaints.

The situation was worsened, he said, by figures showing a 14 per cent increase in complaints from people claiming they were not properly warned that they had breached their data limit.

“We’ll be watching this issue closely,” he said, adding that the overall results were encouraging.

For the first time, the Ombudsman also estimated the number of complaints relative to overall telco services: 313 for every 100,000.

“The clear trend over the past three years is fewer complaints per services in operation, with more services and reduced complaints,” Mr Cohen said.

Victorians had the most gripes, at 1.7 per 1000 residents, while Queenslanders made the least, at 1.3.

Most complaints – about half of the total – remained about poor customer service.

The Ombudsman is an independent authority empowered to investigate complaints about telephone and internet services and make legally enforceable decisions up to a value of $50,000.