Capricorn, I was charged £12 for late payment on a December statement which I never received (and on which I didn't realise I still owed a tiny amount). I rang them and they said that as long as I paid today (which I did) they are refunding the £12.
The call shouldn't cost much, most have 0845 or 0800 numbers, but I can tell you now that they will only speak to you if the lady is there beside you, and if you can put her on the phone to confirm to them that you have her permission (and they will probably ask her a few identity questions to make sure that she is who she says she is, that's quite normal). Some of them will be working over the weekend. It's worth a try.