My question involves business law in the state of: NJ

Greetings!!

I'm an S-Corp owner in NJ and have an agreement with Firm A(in VA) to provide services to it's client Firm B(in NJ). As per the contract, Firm A has to pay me within a week after receiving payments from Firm B to which I provided the services.

The project was completed few months ago and Firm A has received the payments from Firm B. However, Firm A is now not paying me for the last few months since the project already completed. I gathered proof from Firm B that they have made the payments to Firm A.

Questions:
1>What are my options to collect my payments?
2>The agreement/contract between us was not signed, but the terms were agreed via corporate email through it's officers. Can I hold them to that and file a suit?
3>if Firm A intends to close it's operations soon, can they escape the suit?
4>Can I file a lawsuit on my own and in which state?

Thanks in advance for your replies.