tess_yvonne i buy tenner top up a month and usually it lasts but for past few months my data keeps disappearing
If you're paying £10 per month, you should be buying goodybags instead of top up (PAYG) credit. £10 as a goodybag will give you 6GB of data. A £10 PAYG credit will give you only 200MB.
So in future, please make sure you buy goodybags which you should always do starting from https://giffgaff.com/buy/goodybag, or for voucher paymetns only you can dial 43430 and choosing option 2 not option 1. In both cases, do not add credit first because that's what causes your phone to use up some of your credit before you can buy the goodybag.