@jorgeortioneto ,
since you are not an employee of the US entity, you are NRA, the actual work is carried out abroad and there is no tax treaty contravening general IRS position ( income is sourced to where the work is performed ), the US entity is wrong in withholding US federal taxes on your active income. The income is not US sourced i.e. it is Paraguay sourced. You do not need to file a US 1040-NR.
Also US entity probably has not been able to transfer the (withheld) federal taxes without an account number -- your tax ID ( SSN or ITIN ).
Please contact the US entity for the refund..
Is there more I can do for you ?
