I was just called on my BT line by this number 0121 708 4055 too.
I answered and was asked if I thought my bank had over charged me.
I said no, and the man hung up, how rude!!
I called the number back and got a message saying something like ocean consumer research.
I've already gone through all the BT options, months ago, to stop these calls but still the odd one seems to slip through.
I hope this helps you out.