I've done a bit of digging on the web, and found a few pages that mention this number:
Apparently the company is "Reclaim 2 Gain": they offer to help you reclaim bank charges in return for a fee. Some people have said that after giving the card number, the company pulled money out right away (between £40 and £100); I don't know the details, but that sounds pretty iffy. If you do want to reclaim bank charges, you don't need to go to a company like that anyway, because all the necessary info is available on websites.
I often get cold calls on my landline if I'm at home during the day, e.g. "You've won a free holiday!" or "Would you like to save money on your bills?", but it's unusual to get them on my mobile. So, this is just a quick public awareness post: if I get any calls like this, I'll just say "That's none of your business" and hang up.