Paid upfront for investigation & no feedback

I contracted with this company to do an investigation as they came recommended to me. I had to pay a large sum of money upfront about 5 months ago. However, now I am trying to follow up and I am getting no response. I phoned the guy two weeks ago and he said he would phone me back in 5 minutes. However, he never did. Now he is not answering the phone when I call, not responding to texts and also not responding to e-mails.