MPs have criticised General Motors over its handling of a recall last year after hundreds of Vauxhall Zafira cars caught fire.
At a parliamentary hearing, members of the Commons Transport Committee said the carmaker had treated some customers like "second-class citizens".
They also said there had been inconsistencies in GM's investigations of the fires.
The firm apologised and said it was working to compensate owners.
More than 234,000 Vauxhall Zafira B cars were recalled for a second time last year over a technical problem that had caused some models to burst into flames.
Vauxhall initially said the blazes were caused by improper repairs to the heating and ventilation system but later found a fuse design was also at fault.
Evira Toelkes, vice-president of quality at GM Europe, told MPs the firm had written 1.2 million letters to owners seeking a recall and managed to fix 165,000 cars.
She also said that extra technicians had been deployed to speed up the repairs.
However, SNP politician Stewart Malcolm McDonald said customers had made numerous complaints about the firm's handling of the process, with some forming a group to lobby Parliament.
"Some customers were made to feel like a nuisance or were met with disgust at dealerships," he said.
"Vehicles were often returned to them with further problems with the heating and ventilation system."
He added: "I can't think of another product in the United Kingdom at the moment where people have set up a campaign group and come to Parliament to try and resolve it."
Helen Foord, head of government relations at GM, said the firm's dealers had since been issued with guidance on how to handle the complaints better.
"Our dealers were trying to make the recall process as smooth and easy for customers as possible, but we understand that might not be the case the whole time and we apologise for the additional inconvenience," she said.
The executives were also criticised for having launched 59 investigations into the damaged vehicles, despite knowing of 287 reported fires.
Thomas Berenz - director of global safety and field investigations at GM - said GM had not been able to access all of the vehicles.
This was because customers had not always given permission to investigate, while some vehicles may have been scrapped, he said.
Correction 6 March 2017: This story has been updated to give more detail on the cause of the fires.