When you phone a number I think that you can put 141 infront of the number you dial (or a landline or mobile - I think) and this will make your phone number undisclosed to the person you call. But is there a way to make your home phone or mobile number undisclosed to everyone that you ring?
Sorry to ask this - but someone seems to have done this to my mum's phone. And I am not sure how to change it.
Just to narrow this down a bit, is your mum's phone a landline or a mobile?
To save a lot of posts, please post the make and exact model of the handset.
Were your mum's number a business number I think one may ask BT for permanent 141; but I don't think it should be possible for a domestic number. Not that I've ever asked. Could be a corrupt setting by BT (or whoever) though.