On return to Auckland, Simovik was shocked to learn she had an outstanding phone bill of $6000.
It's not known how the Pin-lock was hacked.
"I was thinking 'hold on a minute, $6000, are you kidding me?'," said Simovik.
She was surprised Vodafone had asked her to pay for the thieves' calls and data usage, and questioned their level of fraud detection.
"If a credit card gets stolen, my bank would cover it because they have insurance," said Simovik.
"I don't know why they didn't tell me or why there wasn't a limit. That seems ridiculous to me."
Standard travel insurance does not cover fraudulent use of phones or credit cards.
Vodafone spokeswoman Michelle Baguley said Vodafone called the phone number when they noticed an unusual spike of usage five days after it had been stolen. When no-one answered the network left a voicemail and barred the phone.
Baguley said Vodafone was not aware of the unusual activity until five days later because the information had not been passed on from the Thailand telecommunications supplier.
Baguley said it was the customer's responsibility to inform Vodafone of stolen phones so they could block the account.
"It's in our contract. Vodafone advises all our customers to notify us as soon as they realise their phone is gone, even if they suspect it is only lost, and the phone will be instantly barred," she said.
Vodafone initially offered Simovik a 30 per cent discount, leaving her with $4200 to pay.
However, after enquiries from the Herald on Sunday Vodafone said it would negotiate further when her final bill arrived next week.
Advice for travellers
Avoid taking your phone overseas but if you have to, do the following:
* Use a local Sim card bought from the country you are in.
* If you stick with your New Zealand provider, contact them to deactivate roaming before you leave.
* If your phone is lost or stolen, inform your provider straight away. They will be able to bar your Sim and stop calls and data.
* Inform local police department and get an incident report.
* Use the security lock code, or Pin feature, to lock your phone. This will make it less valuable to a thief and deny them access to personal numbers stored on your Sim card - although it does not prevent the Sim from being used in another phone.
* Check your travel insurance, so you know what you are covered for, before leaving NZ.