The TIO has typically considered retailers responsible for the relationship with the customer and largely for resolving complaints - even if the issue was caused by a wholesaler up the chain - and are charged if the ombudsman receives a complaint from their customer.

The NBN Co and other wholesalers could also be required to pay, after the Independent Review into the TIO found it should have greater control over carriers and wholesalers.

Sometimes, the fees incurred by retailers exceed the revenue from the customer involved, which the report found was a source of frustration for small providers.

"Small telecommunications providers do not have the commercial ???muscle' to recover the amount of these fees from the company up the supply chain responsible for the problem that gave rise to the complaint," it said. In one situation a provider said it spent 60 hours a week handling NBN Co-related complaints.

The review pointed to Fairfax Media reports of a customer caught between the NBN Co and Optus without a landline or internet for four months as an example of how complaints can involve both wholesalers and retailers.

The TIO had already planned a pilot initiative to directly engage with the carrier and immediate wholesaler, such as the NBN Co.

This involves identifying stuck complaints where the retailer advises they are waiting on action by the wholesaler, requesting the wholesaler verify information and engage with the retailer and, if it remains unresolved, involving all parties to resolve the complaint.

But the review said a "more far-reaching solution is required".

Among these recommended changes was to levy a fee on the wholesaler when they are involved in the complaint.

Under the current structure, the TIO levies fees on the retailers.

A submission from the Australian Communications and Media Authority recommended that if the root cause of the problem was at wholesale level, the TIO should be able to make a determination that binds the wholesale provider. This could be requiring the wholesaler to compensate the customer or reimburse the retailer.

"Arguably, the TIO should also be able to apportion its complaint handling costs to the party or parties best placed to resolve the complaint," it said.

It said this additional cost would be "likely to strengthen the incentives for wholesalers to address problems promptly even without TIO intervention".

The review did not agree costs should be apportioned, instead recommending charges be levied to the wholesaler in addition to those already paid by retailers.

It noted NBN Co's submission "took the opposite approach, proposing greater ???clarity' that the TIO's complaint resolution focus is on the retail services provider not wholesalers".

But the review found the current system "has not kept up with the increasing complexity in the supply chain and is not working either for telecommunication providers that only operate at the retail level, or for consumers".

The review also said it was not the TIO's role to oversee the performance or roll-out of the NBN, but that it should use complaints data to find systemic problems.

"So far as we understand, this has not happened in relation to national broadband network complaints and in our view, this is overdue," it said.

The TIO supported both recommendations, and said it would consider the approach to fees on wholesalers once its funding review was concluded in 2018.