Monetary Dispute

Hi,

I am seeking for some legal advice on this matter. A friend of my girlfriend, persuaded her to invest an amount of money in a small business he was doing, and he prepared a written agreement stating the investment amount, investment return, and conditions of fund withdrawal. The amount stated initially was RM7000, but then my gf felt abit insecure to invest that amount and requested to lower the amount to RM5000. It was verbally agreed. But then things did not turn out accordingly. The promised investment return did not materialise. She got her dividend late and the amount is lesser than the promised percentage of return. Felt cheated, my gf requested for a refund. It was stated in the agreement that he will return the full amount within 45 days. But her friend kept on dragging, giving many excuses to delay in payment. After months of chasing, my gf receive the first RM1000. After a few months, another RM3000. So there is another RM1000 in balance, but her friend is starting to ignore her calls, sms, facebook msgs. My question is, does the agreement has any legal power, that if the friend refuses to pay the remaining amount, any legal action can be taken? And my other concern is that, the investment amount agreed in the written agreement is RM7000, but amendment has been made verbally to RM5000, will it affect the legality of this written agreement? Advices would be very much appreciated. Thank you.