Optus is still feeling the ill-effects of the cyberattack it suffered late last year, with the telco’s customer growth taking a hit in the six months to March.

Chief executive Kelly Bayer Rosmarin on Thursday said while the cyberattack had interrupted the company’s momentum in the second half of the year, subscribers were coming back to the telco.

“We really have taken accountability for what happened, apologised and worked hard to regain trust with our customers and market, and I think our efforts have been recognised and that’s why you see the return to growth,” she said. “Had it not been for the cyberattacks, we would have expected our results to be even stronger.”

During the year, Optus added 425,000 subscribers to its mobile customer base, but about 304,000 of that was in the first half. Net subscriber growth was less than half that figure, at 121,000, from September to March.

In September, Optus’ systems were breached in one of the largest cyberattacks in Australian history, accessing personal details of millions of the telecommunications giant’s customers.

Rosmarin said it was “towards the end of December” that Optus returned to a net customer-positive position.

Most of the growth came from new rather than returning customers, with the return of travellers, students and migrants helping bolster Optus’ numbers.

Average revenue per user (ARPU) – a key metric for telcos – remained mostly flat across the year despite price increases. Revenue was subdued on the back of a greater proportion of lower-paying prepaid customers, lower domestic wholesale roaming and a decline in handset insurance revenues after that business was sold.