I have just had one of these calls. on 1471 the number is showing as 001234567890 There was no one there when I answered and then the call disconnected.
The one I had prior to this call was the same number and during that call I was informed that my bank had identified that I had been overcharged £700 in overdraft fees and if I gave my bank account details it would be refunded immediately. I asked the guy what bank he was representing but he said he couldn't tell me because of the Data Protection Act.
Pity I have never had an overdraft, I could have been £700 better off.
It's a shame when these calls come just as I get settled down for a rest 'cause I love winding the callers up. My deaf routine really gets them frustrated.