Revenue Group review: harassment

I have no outstanding debts, especially not medical debt. They've called and left messages once or twice a week for the last few months from the number (44) 528-1348. Unfortunately, they're not on the BBB website, so I can't file a formal complaint, and I don't want to give them my address or any other personal information on their website contact form lest they harass me in a different way. I can't afford legal help, either.