This number is Nationwide Debt Direct. As far as I know they only call people from this number who are their clients. Perhaps anyone who has gotten calls from them have a relatively new number and NDD is trying to call someone who formerly had the number?
I just received two calls in quick succession from that number and was going to ignore it ("Unknown Name"). The second time they called I was trying to enter the number in bing to do a search but decided to just grab the phone and answer it. I am a client of theirs, so they had a legitimate reason to call me. They are a company which signs up people who are in over their heads in credit card debt, and when you have enough money set aside they negotiate with your creditor(s) to settle your debt for a much lower amount.
Some decades ago one of my friends was in real trouble financially. He told me he was in some kind of thing through which he paid off all his credit cards but did not have to pay the full amount. I could not comprehend what on earth he was talking about, but now I'm finding out.
P.S. The types of call listed below did not fit what NDD is, so I left it on "unknown."