If your company deals with the banks in prohibited transactions, then you did well to leave this job. But you were wrong to train others on such transactions. You should have explained the Shar`i ruling. If the trainees responded positively, then praise be to Allah, and if they did not, then you have still done what is required of you.

Islamic banks are based on permissible transactions such as selling, buying, profit sharing, partnerships and other Islamically-acceptable forms of investment. The interest-based system on which commercial banks are based is a prohibited system that is based on lending and borrowing with Riba.