Guy Ward's excitement about an Optus broadband and phone bundle upgrade for $5 more each month quickly dissipated when he noticed his internet speed had slowed.

The business mentor from Melbourne was checking his data usage online in April when he realised Optus had cut the download speed from 100 Mbps to 30 Mbps.

"Optus never mentioned the change in speed in the letter they sent to us or in the first bill we received," Mr Ward, who is on a hybrid fibre coaxial network.

"My complaints fell on deaf ears. They tried to keep it a secret. This was surely misleading and deceptive conduct."

Mr Ward's case points to the broader problem about slow internet speeds and the lack of transparency over the quality of broadband services, such as speeds and webpage load times, which can vary depending on the provider and the customer's area.

The latest statistics from the Telecommunications Industry Ombudsman reveal slow data speeds accounted for 20 per cent of the 11,000 internet-related complaints in the first quarter of this year, followed by unusable services and connection delays.

Complaints about slow data speeds jumped by 66 per cent on the previous year's figure. The Ombudsman's spokeswoman said they couldn't comment on the possible causes.

The figures back survey results from the Australian Communications Consumer Action Network, which found 70 per cent of respondents had unsatisfactory experiences with their broadband services - the top trigger being sluggish speeds.

An ACCAN spokesman said the absence of information on the quality of different broadband services made it hard for consumers to judge the performance, especially prior to signing up, highlighting the urgent need for a national monitoring system.

"If they are experiencing poor quality services, broadband monitoring data would help consumers to identify what the issue might be and whether their provider is performing.

"It is almost impossible for consumers to know what is affecting their broadband.

"In this situation a consumer may choose to switch providers, but without broadband performance data it is impossible for them to know if this would be a good decision," the spokesman said.

ACCAN is calling on the Federal Government to implement the broadband monitoring program trialled by the Australian Competition and Consumer Commission last year, which would allow the watchdog to verify telcos' speed claims.

Mr Ward says Optus ignored his complaints, refused to acknowledge the dramatically reduced internet speed and offered him $30 "compensation", until he lodged a complaint with the Ombudsman.

He was on a bundle plan that was being "closed down", and transferred onto a new plan with increased monthly download to 200GB for $5 more a month.

An Optus spokeswoman told Fairfax Media it "made an error" when Mr Ward was transferred to the new plan and it had resolved the problem.

"Optus is making changes to its technology systems which will provide customers with simple, integrated billing for all their services," she said. "As a result, we are closing down some of our older plans and moving affected customers to newer plans."

Mr Ward believes tens of thousands of customers may have been similarly affected, but it would be difficult for them to detect the change because of the lack of transparency about data speeds.

He believes the contract migration was a result of Optus selling its hybrid fibre coaxial network to the National Broadband Network, and having to adjust its products.

An ACCC spokeswoman said it was in the midst of securing funding for the broadband performance monitoring program, which it believes will boost transparency, promote competition and help consumers.

"The costs of running a broadband monitoring and reporting program are modest - to illustrate, if a program were to cost say $1 million per annum to run, then this would equate to around 15 cents per broadband service a year," she said.

But peak industry body Communications Alliance, which estimates the "ineffective" program will cost $10 million, says consumers will ultimately pay.

Its chief executive John Stanton says similar tools were already available, such as Netflix's ISP Speed Index.

"A whole range of factors can contribute to dissatisfaction with data speeds, things like the transition to an NBN-based networks, the greater availability video streaming, the greater number of devices being used in a household," he said.

"We're not convinced there's a market failure here. We should make use of available tools and less intrusive strategies, such as crowd-sourcing."

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