Medibank customers appear to be the most dissatisfied, with complaints to the Private Health Insurance Ombudsman skyrocketing in the past three years.

Three hundred-and-fifty complaints were made against Medibank between January and March this year, 127 per cent more than in the same quarter in 2014, the ombudsman's latest quarterly bulletin shows.

To compare, total complaints against all health insurers grew by 18 per cent in the same time frame.

Also, Medibank slightly lost its grip on the market over the period, with its share slipping to 28.6 per cent.

Its key competitors Bupa, HCF and NIB each managed to significantly slash the number of complaints made against them to the ombudsman.

Medibank was privatised by the Federal Government in November 2014.

Last month, the insurer was accused of misleading policyholders by failing to notify them of slashed coverage for common hospital tests such as X-rays and CT scans - as part of its attempt to boost profits ahead of the $5.7 billion public float.

Fairfax Media earlier reported at least 30 impacted customers had lodged complaints with the ombudsman, only to be told to go back to Medibank, which it said was in the right.

One of the complainants was Sam Harrison, a TAFE teacher from Melbourne, who said she was "furious" when the ombudsman referred her complaint about an unexpected $256 hospital bill back to the insurer late last year.

After she lodged a second complaint on the same matter in June, the ombudsman ruled in her favour, saying Medibank had provided the office "incorrect information".

"I have been advised by the ombudsman after re-submitting my complaint that they have accepted it, and as such I will be reimbursed for my out of pocket expenses," she said.

The latest quarterly bulletin shows 63 complaints about Medibank were escalated to "dispute" status - nearly triple the number in the same quarter in 2014.

It's understood most are related to waiting periods and "standard charges".

Overall, the ombudsman was dealing with 164 disputes, with 45 per cent about information (for example oral advice and lack of notification), followed by benefits (hospital exclusions and restrictions) and waiting periods (pre-existing conditions).

An ombudsman spokesperson said it couldn't comment on escalating complaint and dispute figures relating to Medibank.

"A range of factors may influence individual insurer complaint numbers during any given quarter," the spokesperson said.

"The ombudsman provides complaint analysis and guidance to insurers directly to address systemic issues and may raise specific issues with other Commonwealth agencies."

The quarterly bulletin shows most of the 1025 complaints related to premium increases, confusion by advice received over the phone and at branches, and membership cancellations.

Medibank did not directly answer questions about the big jump in complaints but instead commented on the jump in premium increase-related complaints.

In regards to addressing this, she said: "Medibank has proposed a number of reforms to improve affordability and value of private health insurance, including prostheses pricing reform, improving information sharing for consumers and insurers, standardising simpler products and terminology, and improving competition and premium setting."

She said its 3.8 million customers were the "absolute priority" and it aimed to provide "outstanding value".

"We have been and will continue to invest in improving our customer experience," she said.