Telecom Xtra says it has now restored full internet services and apologises for problems over the past few days.
It is also addressing the question of compensation for affected customers.
Thousands of Xtra customers have been unable to access the internet at various times since Sunday because of technical problems.
In a statement on Telecom's website, customer care manager Kelly Moore said staff had been working "around the clock" to fix the problems.
"Services were restored to nearly all Xtra customers Tuesday evening. However some customers may have experienced difficulties throughout Wednesday.
"We sincerely regret the inconvenience and frustration that has been caused to our customers over the past few days."
The cause of the fault was still being investigated.
Mr Moore said customers still experiencing connection delays should restart their computers and modems.
- NZPA
Internet services 'restored' to Xtra customers
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