All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Riba (interest and/or usury) is forbidden in all places and at all times except in dire necessity. Those who said that Riba is lawful in the Land of War are wrong. So, if all the transactions of this company are based on Riba and unlawful dealings, it is forbidden for you to work in it even if you are only a broker between this company and the companies that sell goods to it.
If its transactions combine that which is forbidden and that which is lawful, then you are allowed to work with it if you could limit your work to the lawful dealings only. It is unlawful for you to work in Riba even by writing a note or carrying it or helping in it in anyway.
Always remember that Allah Says (what means): {And whoever fears Allaah—He will make for him a way out. And will provide for him from where he does not expect. And whoever relies upon Allah — then He is sufficient for him.} [Quran 65: 2-3] You should also remember the saying of the Prophet “You do not leave anything out of fear of Allah, except that Allah gives you what is better than it.” [Ahmad]
Allah Knows best.