EE will issue refunds worth 1 million to a small number of customers who overpaid VAT on international data charges.
The money reportedly went straight to HRMC rather than being given to EE and the network told the BBC that it wasn't the company's fault, but down to an administrative error.
EE spokesman David Nieberg said: "Due to a configuration error in our billing system, made following a system change, a small number of customers were wrongly charged VAT on the Data Roaming bundle outside of Europe.
"This was a mistake, and we are now refunding these charges and contacting affected customers to apologise for the error."
EE said it has now recouped the money from HMRC and will issue refunds of between 2 to 80 per incorrectly billed customer, which only represents 0.5 per cent of all EE's 28 million customers.
The refunds will be applied directly to the bills of affected customers rather than into bank accounts and each of the customers will be advised of the mistake by text message.
The VAT was collected from customers who used data while roaming outside of the EU between October 2012 and October 2014.
EE said the problem was flagged by one of its customers and acted immediately. Any old EE customers who used data outside of the EU who believe they may have been charged are being told to contact EE's customer service department to organise a refund.
EE's 4G network now covers 7.7 million in the UK, although news broke at the end of last year that the company may be acquired by BT for 12.5 billion later this year.
