Over a million customers were left with no service on October 12 after "network nodes" failed.
Around 10% of O2's 16.3 million UK users faced difficulty connecting to the network to make calls, send texts and use the internet during the downtime.
O2 has now outlined its strategy to combat the issues, promising to invest £10 million and ensure the "highest level of customer network experience" following a similar, more widespread incident in July.
In a blog post titled 'Rebuilding your trust in our leading network', O2 boss Derek McManus said: "We are extremely disappointed to have let our customers down again. Two network faults in a short space of time is unsatisfactory.
"Despite industry-leading technology and major investment in our network, we recognise we need to take immediate action to address this specific problem.
"We are removing the Central User Database provided by one of our suppliers, which has suffered two different faults in the last few months. We are not prepared to risk this happening to our customers for a third time and are implementing a proven alternative solution.
"We will be committing an additional spend of £10 million on this change, and will also continue to invest £1.5 million a day on building out and improving our network.
"While we recognise that we have dented the confidence and trust of some of our customers, I hope this plan will demonstrate our commitment to rebuilding that trust.
"We will not rest until we have cemented the stability of our network and can deliver the level of service customers have come to expect of us over the last ten years."