Issue with non paying company

Hello, I am writing from Singapore. I have a situation here that i hope some professionals here can advice me on.

I have been a sub contractor for the installation of IT hardware and services for a company ( Lets call them company A ). - Note : i'm not the only one - there are quite a number of installers from company A too.

Just very briefly : The usual procedure are for IT installers ( from my company and Company's A installers ) to go to the warehouse of company A to draw stock for the day - and then proceed for the day's IT installations. However - Company A does not have a full time stock man in the warehouse - neither does Company A keep track of any equipment being withdrawn or returned.

Now additionally:

We started in September 2007 and over a verbal agreement that our invoices will be settled within 60 days after the end of each month. Eg: September's invoice will be settled in November.

However Company A has delayed payment repeatedly and instead of releasing the full amounts, they have been paying just partial of the invoices. Now its April 2008, and they've yet to clear their invoices for November 07, December 07 and Janruary 08.

Now this is where it gets a little complicating.
Lately, we've just pressed Company A for payment and we were told that Company A has realized that they are missing some equipment and are refusing to release the payment until they have deducted the cost of the missing equipment from the amount they owe us.

I would like to find out : Can i demand for my payment? And am i liable for the loss of any equipment that Company A has incurred ? ( Bearing in mind that Company A does not have an official stock man to monitor the movement of stock and that we are not the only people with access to the warehouse and that they do not have any documents showing that we have taken the missin hardware?)

Many Thanks!

I forgot to add : The amount owed amounts to about $20,000

[reallylight]

Did you not have a contract bond in place to ensure that things were completed in a timely fashion and indicating exactly what was to be done and by when?

Hello, thanks for the response.
No - everything was done verbally - we were told what to do and we just fulfilled our duties ( big mistake on our part , we should have came up with a contract )

Thus is there anything we can do now?