Lack of Competent at Intec

I am registered with Intec college for a Higher diploma in Mechanical engineering, my bad experience is that I wrote a subject called management 2, and I failed twice only to find out that they didn't mark my assignment for that particular subject, I have been querying for this for a year now, and the company need the prove soon that I complete my diploma. This year end I am supposed to write my last subject again is not happening because they call me and say they didn't receive my application for writing exam hence i send the prove to show that i did apply, but no answer till now. and exam is closer which lead to not to write my exam. This is so frustrating, I need help.