SAFE88,
what interview did you fail? There are 3 interviews?
Don't you think you need to give a little bit more information if you want a serious answer to your question? Rather than just blurting out "what can I do better".
If I was to second guess the particulars of your application, you would have failed by making the same mistake all other CPL/MEIR make when applying for CPP - that is thinking you have the job in the bag at Stage 1.
CPP is for 0 hour pilots but we have many with upto 800 hours who have gone on the course. Now obvioulsy, a 0 hour pilot will not be asked a CPL standard Flight Planning question. Likewise, we will not ask a guy of your calibre something silly like what are flaps. You will be asked questions based on your experience.
I have heard that there have been numerous occasions when a CPL ME/IR gets into a hot sweat when asked whether Induced Drag and Profile Drag increases or decreases with speed.