Complaints against roaming service more than doubled to over 1,200 cases in the first eight months from a year ago after the border reopened following three years of pandemic, Consumer Council figures show.

The council said that in one case, the complainant was charged more than HK$10,000 for using the roaming service.

Surnamed Fong, the complainant made roaming calls on her Hong Kong mobile number during her stay in Canada between January and February.

She was first charged HK$170 in March for her seven-minute roaming call in January and HK$4,900 in April. She said she had spent 160 minutes talking on the phone in February.

Fong stopped the roaming service in March, but was charged HK$5,050 in May with the bill stating she made a 165-minute roaming call on February 27.

The operator explained that the delay was due to dilatory data roaming usage from the service provider in Canada.

Fong was upset with the explanation for the delayed bill as the delay could mislead users to keep using the roaming service without knowing the whopping charges.

The telecom provider offered the complainant a 20 percent discount on the bill following the council's intervention, and deactivated the roaming service of her account.

The council suggested one may use instant messaging apps to make calls when travelling abroad.

"If someone has already purchased data roaming plans, they may consider using instant messaging apps with the same mobile number," said Victor Lui Wing-cheong, the council's research and testing committee vice chairman.

Alternatively, people may buy a day pass for making roaming calls, Lui said. But he called on them to mind the time difference between Hong Kong and their locations as the dates may be calculated variously.

Meanwhile, the consumer rights watchdog hit out at the aviation industry, citing a lack of transparency for the compensation of lost or delayed baggage.

It said passengers could wait up to 45 days before claims are processed on a "depending-on-circumstances" basis.

The council surveyed 22 airlines on their baggage compensation policies after receiving 61 complaints in the first eight months - a surge from 14 cases from the same period last year - since normal flights resumed.

Council chief executive Gilly Wong Fung-han said: "Although the number of cases was not that much, the increase was significant."

It found that the cash allowance for delayed baggage could vary significantly - from HK$237 to HK$1,777 - with airlines imposing different requirements for eligible claims.

The council cited a complaint from a couple whose luggage was delayed on a trip to Madrid, Spain.

The couple had to buy daily supplies for about EUR1,200 after carrier staff said there was no threshold for the purchases.

But the carrier later told them it could only compensate EUR400. The complaint is still being processed.

"International air travel passengers are typically protected by the Warsaw Convention or the Montreal Convention," Lui said.

He reminded that passengers should check which convention applies to their destination when making claims.

Roaming-service complaints double after border reopening