Under what laws can I send a legal notice to the website Co?

We are a website design agency and after designing our client's website, we gave it to a website development company to write the software and make it functional so that people could subscribe to the magazines of our client. At the start, it was decided that two months would be needed to design and develop the website. One month for the designing agency to design the website and one month for the development agency to write the codes/software of the website. But instead of a month's time, the development company took more than 4 months. After paying 90% of the money, the developers haven't yet given us the emailing module yet by which the customers are supposed to get intimation on their registering for a trial offer or taking paid subscription to a magazine.The developers have also not handed us over the codes of the website. My clients, who are a Singapore based company, have had to bear a huge loss as they have not been able to monetise the magazines for the past 4 months.We are not only facing huge embarrassment but this is becoming a bigger embarrassment to our client. Under what laws can I send a notice to the website development agency and what are the options available to us as an agency. Plus will this come under criminal law or civil law?