Unfilled software development contract

I'm not familiar with India law, but I am with US law. I have a possible dispute that may airse between my company and Daani IT Solution 22A/16A/D1, T.B. Sapru Road Civil Lines, Allahabad-1 INDIA I paid them $4,800 in advance last summer for a development project that was supposed to be complete no later than November 22. Now they are asking me to pay more. I have already paid an additional amount once, and i agreed to make one more payment to them but I'm refusing to pay any additional until I see their completed work. This company provides SaaS for us (a cloud-based compensation management system for our MLM sales division). This is an upgrade to the existing system. If they shut off the server for non-payment when in fact it is them who owe us, it'll cause a great deal of damage to our company. The question: In the event they shut off the server and thus cause damage to us, what would you charge just to put them on notice that we have legal counsel in India and will not tolerate their failure to perform? Thanks in advance for your response. Best Regards, Richard Gaustad GlobalTmail USA, LLC 207 North Main Tooele, UT 84074 website: http://crowdfunder4all.com