The telco experienced a 12-hour outage on Wednesday, which prevented 10 million people and businesses from making and receiving calls, or completing transactions.
Optus has said it will provide customers with an extra 200GB of data to reward their "patience and loyalty".
But Small Business and Family Enterprise Ombudsman Bruce Billson said issues faced by small businesses on the Optus network hadn't been addressed and rejected suggestions by the telco that any compensation for loss would amount to $2 a day.
"The response by Optus is inadequate and not sufficiently dealt with by an offer of extra data," he said.
"Small businesses rely on telecommunications as an essential service, but they have been poorly served by Optus throughout this event and some have suffered a significant economic cost."
Customers, politicians and business figures have criticised Optus over the outage, with the Greens securing a Senate inquiry into the disaster and the federal government launching a review.
In September last year, the company suffered a massive data breach which affected millions of Australians who had sensitive documents, including passport and Medicare numbers, leaked online.
Optus director Matt Williams says the company is working hard to retain customers.
Optus director Matt Williams said the company knows its customers could turn to other phone service providers.
"We really value, very highly, the relationships we have with our customers, the loyalty they have to us, their ongoing choice of us," he told AAP.
"We provide unique and amazing value, as well as features and experiences that our customers can't get anywhere else.
"So we'll continue to provide all those things (and) work very hard to make sure that we rebuild those experiences with our customers and that relationship."
Acting Prime Minister Richard Marles said the telco needed to be upfront about what caused Wednesday's outage.
"Optus really needs to make clear to its customers exactly what happened here," he told Nine's Today program on Friday.
"It's obviously why we've undertaken a review so that we can learn the lessons of this, not just for Optus, but in fact for all telecommunications."
Opposition Leader Peter Dutton said a review would be cold comfort for businesses affected by the outage.
"The level on which we rely now on interconnected society, on these services being up to scratch is phenomenal, and the government needs to work harder," he said.
"(Customers) have a reliability question in their minds now about the service being provided by Optus, and I think they've got a lot of repair work to do."
Under Optus' compensation plan, postpaid users will be eligible for 200GB of extra data and prepaid users will be able to access free unlimited data on weekends until the end of the year.
"We know that there's nothing we can do to change what happened," Optus chief executive Kelly Bayer Rosmarin said.
"We really appreciate the patience and understanding that our customers have shown."
We're very sorry for the outage— Optus Help (@optus_help) We know the importance of being connected and we're deeply sorry that your service was interrupted. We thank you for your understanding and patience while we worked to restore our operations.We're committed to working tirelessly to provide the…November 9, 2023
After the data breach in 2022, Optus funded a credit monitoring service for impacted customers and covered the cost of drivers licence number changes.
Social Services Minister Amanda Rishworth encouraged businesses who suffered financial losses from the outage to contact Optus to discuss compensation.
"I would certainly encourage anyone that has had financial losses to approach Optus, and if they get no joy, go to the telecommunications ombudsman," she told Seven's Sunrise program.
Optus claimed the outage was caused by a "network event" that triggered a cascading failure. Its engineers are investigating the issue.
27°C