I keep receiving calls on my mobile from 0870 330 2525. I've now had about 10 in the last two weeks!
At first I thought it was somebody who needed to get hold of me, so I answered it. both times there was silence.
I phoned the number back today and immediately got an answerphone message saying "Thank you for your call. All our agents are busy. Please hold" - no mention was made of a company name. I hung up!