@ mithun,,,,,,
having backlog is common scenario for most of the students. Computer Science and Information technology are not closely related.BOTH ARE FRUITS but one is MANGO and another is APPLE....so that's a valid reason,,,,, you have to make the VO understand that foreign Diploma in IT will help you to bring a diversity in your career.
the job market is saturated and you need it....
Due to backlogs, your study length has increased. so, i think, VO thought, you had an intention to fail and linger your stay in canada and previously you also applied for PR. it put a question mark to VO's mind about your intention
i advise to make a strong SOP that you can and will finish the diploma within 2 years and it'll help you to get promotions, or better posts in local country.,,,