A pre-paid card which is being marketed to students and young people travelling abroad has been heavily criticised on a website sponsored by the same firm.
Card holders say they have had serious problems dealing with STA Travel Mastercard's India based call centre.
Unlike credit cards or debit cards, pre-paid cards have money loaded onto them in advance.
STA Travel says only a very small number of customers have had issues and some changes have already been made.
Helen from Kent recently finished university, and wanted to go travelling to South America this summer.
She heard about the card when she went to fix her travel arrangements at an STA Travel agency in London.
She paid £20 for it which included £10 which was already pre-loaded. Her problems began when she arrived in Brazil, as she told Radio 4's Money Box programme:
"I found it difficult to obtain money from ATMs. The screen would often say things like 'you're experiencing communication problems'."
Things then got even worse for Helen.
After using one particular ATM in Brazil, she discovered the details of both her STA Travel pre-paid card, and a separate credit card she had used, had both been copied and used to make fraudulent transactions.
Her credit card provider accepted the loss quickly.
In order to try and reclaim the £250 she had lost on her STA Travel Mastercard, Helen had to speak to an Indian call centre which she found a difficult and frusrating experience:
"They struggled to understand English and I had to repeat myself endlessly on my mobile from Brazil. It was really frustrating.
They didn't offer me any solution to the problem."
Things did not improve when Helen returned to the UK. She sent a witness statement and phoned the call centre at least four times to ask about a refund.
Each time they promised to return her call within 24 hours. Helen says each time they failed to do so.
After Money Box contacted STA Travel on Helen's behalf, she received a call within hours from the firm saying it had refunded her both the £250 and the cost of her calls in South America.
The STA Travel Mastercard is issued by Newcastle Building Society, but the call centre which customers deal with is run by Tuxedo Cards.
When Helen looked on the STA-sponsored website travelbuzz, she found there were many other STA Travel Mastercard holders complaining about experiencing poor customer service.
Raffick Marday from the comparison website compareprepaid says he has had similar problems reported to his site:
"We have heard of issues raised by customers about the Tuxedo call centre. The main problem is it seems they're poor on customer care."
Ian Swain, STA Travel's product director, says criticism on travelbuzz and other websites was not representative of most card holders' experiences:
"The vast majority of customers are delighted with the product. We realise that, for a very small number of customers, there have been some issues. A number of changes have been made to reduce future issues."
Tuxedo Cards said: "Tuxedo prides itself on providing excellent customer service. On the rare occasions that customers are not wholly satisfied, we will always endeavour to rectify the situation as quickly and efficiently as possible."
BBC Radio 4's Money Box is broadcast on Saturdays at 1200 BST, and repeated on Sundays at 2100 BST.