Business Dispute

I sold the use of my brand name to someone for an X-amount for Xyears, we agreed to the terms and even agreed to a final draft of the agreement via email. This individual paid the agreed amount to me (the amount was a one time non-refundable fee) and we started the business and told me he will sign the agreement after few days. The Money was spent for advertising and supporting operations. This person kept delaying signing the agreement and I have sent him numerous reminders to do so. Now this person is not signing the agreement and asking for his money back and threatening me (stating he has his ways and influence to get the money back via police and political connections) Please advice what should I do to protect myself and my business from something like this.