Hundreds of thousands of customers with mobile network Three have been told they are automatically being moved onto new, more expensive plans, with many likely to see their monthly tariff double from £15 to £30. But you don't have to accept a bills hike – if you're affected, here's what's happening and what you can do about it.

The mobile giant has sent letters to many of its customers on 'legacy' deals, warning them they will be shifted to a new deal and that they have 30 days to accept the changes or leave Three.

But many customers including MoneySavingExpert readers have reacted furiously to the move, and after receiving complaints Ofcom says it has contacted Three to ensure customers are being treated fairly.

If you've received such a letter from Three, you're free to leave your contract penalty-free and switch to another provider if you wish. See our Cheap Mobiles guide for the top pick Sim-only deals and more mobile cost-cutting tips.

What's changed?

Three's written to all those hit by the changes, which affect those on older tariffs who have finished their minimum contract term and are now on 30-day rolling contracts. Three has 8.8 million customers in total, and while it won't say precisely how many are affected, it's understood to be hundreds of thousands.

  • A series of older tariffs that are no longer sold to new customers are being closed to existing customers.
  • The tariffs affected include the popular 'The One Plan', which offered 2,000 minutes, 5,000 texts and unlimited data for £15/mth.
  • Three says it is moving customers onto "the closest plan to the one they are on". In many cases that means it's switching customers to a plan that usually costs £33/mth for unlimited minutes, texts and data – though those moved across will only pay £30/mth.

Three's letter to customers reads: "We're always working to make sure we offer some of the best plans on the market, with great value minutes and data that helps our customers get the most out of their phones. But to do this, we have to change our plans every so often.

“As your minimum term has ended and the plan you are currently on is being phased out, you will need to change to one of our new plans. But there's no need to worry, we've got a great range of new plans to suit your needs.

“We're writing to let you know that we plan to transfer you onto one of our new plans which most closely aligns with your current plan allowances.”

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Anger from users

Many Three users have expressed anger at the changes, with some venting their frustration on Twitter and using Three's marketing hashtag #makeitright. Here are a few examples of the tweets we've seen:

Ofcom says it's received a number of complaints as well. A spokesperson said: "We are aware that some consumers are unhappy following Three's decision to phase out some of its older price plans. We have contacted Three for further information to ensure customers are being treated fairly."

What can you do if you're affected?

If you receive a letter from Three, it's important to understand you DON'T have to accept a bills hike.

  • You can switch to a new tariff or leave Three for a different provider penalty-free. But you must contact Three to let them know you want to leave within 30 days, as otherwise you'll be automatically moved onto a new 30-day rolling contract. You can phone Three's customer services on 0333 300 3333.
  • You may be able to haggle a better deal with Three, particularly as you're a long-standing customer and can move penalty free. See our Mobile Haggling guide for tips.
  • It's worth benchmarking Three's deals against those of other providers. We've full info on how to do this in our Cheap Mobiles guide.
  • If you're unhappy with Three's decision, you can try complaining to Ofcom, as others have done (see below).

What Three says

A statement from Three says: “In March 2014, we introduced new price plans giving customers more options in the size of their data and voice bundles, as well as limits and alerts to prevent bill shock.

“We have a lot of tariffs that we no longer sell and moving customers to one of the new plans will ensure they can enjoy the benefits of these plans.”

Additional reporting by the Press Association.