Roughly 55,000 Vodafone customers will be able to end the contracts early following an investigation by telecoms regulator Ofcom.
Earlier this year Vodafone introduced new international roaming charges for a number of countries outside the EU and informed customers by text.
The Roam Further charges meant customers were charged a flat fee of £6 a day to use their phone in 60 countries. However, users were charged the £6 fee even if they only sent one text message.
Following complaints from customers, Ofcom ruled that mobile phone networks must give customers 30 days’ notice of any contract changes likely to be of “material detriment”.