Kimberley explained how her in-laws had to go to The Warehouse to buy sleepwear, while her sister-in-law drove to New Plymouth the next day to collect them.
"It was supposed to be a special holiday for them, but instead they ended up in an upsetting situation and feeling embarrassed," she said.
Kimberley said the family contacted Intercity in order to retrieve their belongings, but had subsequently spent two months being "passed around in circles" without any resolution.
"Two months later we were given a claim form which was invalid as it needed to be lodged within seven days of the travel," she said.
"We went to the police and our insurance company but they questioned why it had taken so long to report it - but it was because of the process by Intercity."
Kimberley told the Herald her in-laws lost a combined total of $4,170 in belongings, including winter jackets, shoes, sunglasses and glasses, and hearing aids.
Despite the company website stating it may take up to 10 working days to investigate lost carry-on luggage or items, the couple didn't get a resolution until 72 days later.
After being contacted by the Herald, Intercity apologised for the delay in resolving the complaint and said an internal investigation had been launched.
"I can confirm that today our customer service team have been in contact with Kimberly. We will be undertaking the following actions to compensate [the couple]," a spokesman said.
He said the couple would receive a full refund of the bus fare, $2,670 compensation for contents of their lost luggage, and $250 compensation for the insurance excess required for the hearing aids that were in their luggage.
"Again, we are sorry for the delay caused in resolving this matter," he said.
Kimberly confirmed she had been contacted by Intercity and said she was relieved at the resolution.
"My in-laws are really happy, and now we can replace all their items - so they are over the moon.
"My mother-in-law has been in hospital having some bad luck, so she feels like their luck has turned," she said.
Kimberly said the drawn out process had been very frustrating.
"I was getting really frustrated and losing sleep over it because everyone was upset.
"Hopefully they improve their processes after this because if we have tourists coming to New Zealand and losing their luggage because of the bus drivers then it's not a good look for our country."