employer demanding resignation despite performance.

I am in sales working for a company for more than a year in sales department. I got my organisation good orders which my immediate supervisor is basking in and making merry while I have been asked to repeat the same performance else leave. I wonder how my seniors job can be secured and not mine when the credit for this order goes to both of us. I presume that my senior has also shown me in bad shape in front of the directors ensuring his job is saved. Kindly suggest what steps can I take to save my job. Also how do I ensure that the actual credit comes to me and not my seniors. Kindly suggest the legal course.