MOST mobile customers on SIM-only deals are overpaying for unused data, Citizens Advice has warned.

Short of more mobile networks giving refunds or making it easier for customers to reduce their monthly allowance, here are some tips on how to avoid overpaying for data:

1. The first place to start is by checking your data usage against your monthly allowance. This should be included on your monthly bill. Contact your provider and renegotiate if you are using less than you are buying. Most SIM-only deals are on a monthly contract so they are usually flexible to change to a cheaper option if necessary.

2. Remember that the switching process for those on a SIM-only deal is easy and moving your number will only take a few hours.

3. Those who are on a handset deal and tied into a contract could ask ask for less data and more minutes, for example. Try to negotiate a better overall package.

4. If your provider is not willing to give a discount and you are out of contract, do not be afraid to vote with your feet.

5. Price comparison websites are also useful for finding a tariff that better suits your data usage.

6. If you are using wi-fi at work, on the train, in coffee shops and at home you may well not be using all the data you are paying for each month. You only use your own data when you are not on wi-fi.

7. If you want to find out how much you are paying for your package compared to other people on exactly the same deal, go to ismybillfair.com and find out in 60 seconds. Use this during the negotiation process.