What are the ways of protecting your salary while working as a freelancer?

I worked for a company day and night and my services were rendered for 4 months, day and night.

They were suppose to pay the fees of 4 months together when everything was finished from the group up. ofcourse i took care of every single on their website, tv commercial, graphics, seo and social media. and you are sure how long does it take to single to take care of final touches.

Now here is the moment of truth after 4 months when i sent an invoice of $4000 they locked me out of the ftp, cpanel and client portal and stopped to respond back to my emails.

I don't have any other way to generate my revenue. i am married , i have a family to run and all have been effected by that. i am under so much of stress now.

So i have rendered by services and didn't even get a single penny.

Ofcourse we didn't signup for a physical contract, company is from Arizona USA and i reside in Pakistan. this company was came to me through my old very good contact.

What can i do here to defend myself and get my funds from them? i know i can always hurt their company reputation through google, reviews and launch website against them but what i am looking for its the funds which i worked for.