Can a company that has filed bankruptcy, claim from vendors money paid for services provided to them?
I did some cabling jobs for this company, I received a letter from their attorney saying that I have to pay back like $16,000 to this company. IS THAT LEGAL? The company filed Chapter 11 bankruptcy. What can I do.

You need to contact a lawyer of your own.
The letter you are getting is saying the company didn’t have the right to pay you (hence they want the money back), which would make you yet another unsecured creditor hoping to get pennies on the dollar.