Need advice

Generally, your chances for an interview are much greater if you are physically present in Singapore. Most companies do not consider applicants without Singapore phone number and wants to pay for your travel to an interview. If you are serious about looking for a job in Singapore, you should come here for a few months. Job-search on SVP (the standard visit visa) is allowed.
If you cannot afford that, come for a shorter visit and indicate in your prior applications "I will be in Singapore from ... to ... and this would be a good possibility for a personal discussion."
The second hurdle is the work visa, which is very difficult to get (especially for ethnic Indians, which Sri Lankans are counted as) and thus many companies won't consider foreigners who don't already have one. If you are currently earning above S$8000, apply for a PEP (Personal Employment Pass) - the only work pass you can get on your own merit without already having secured a job in Singapore.
Even then, don't expect to receive many replies: Singapore companies never send rejections - they think no answer is enough.
Last but not least: As everywhere, personal contacts help a lot!

Hello

Welcome to Expat.com!

You can read these articles on Work in Singapore as well. It may help.

Good luck in your research,
Aurélie