How do I re-claim money that is owed to me if the other party refuses to return it?

Prior to my conversion to Islam, I was in the company of a semi-practising Muslim brother. He asked to borrow £100 pounds citing financial difficulty. I lent him the money. Soon after my conversion,I lent him a further £150, at his plea. He stipulated that he would re-pay me when he could. Upon the completion of my degree, when I was being forced by my parents to leave Islam and return forcibly to my home in Singapore, this brother once again asked to borrow £650 to pay his rent. He asked for this money in the name of Allah. I conducted a bank-to-bank transfer for this sum although I was cash-strapped myself. Nonetheless,I was sympathetic and concerned as he was a fellow Muslim, although he used to discourage me from observing hijab. During this time, my husband had asked for my hand in marriage. This brother who had borrowed money had asked me my hand in marriage. I refused as he was not a practicing Muslim. When he found out about my husband?s proposal, he resorted to back-biting and generating ill-feeling. When he found out I had contracted nikah with my husband, he contacted my husband, parents and in-laws, tarnishing my name.My husband and I wrote him 2 letters, requesting the money. Upon requesting the money,he flatly refused.I have been very upset as I feel I have been cheated of my money. and cannot allow a lying, deceitful, hurtful person to benefit from this. I understand that Allah(SWT) is divine legislator but as Allah?s slave, how can I ease the situation?