If everything is perfect than your application wouldn't be refused twice. So I think your IELTS raises an red flag to the vo. What your school accepted again has nothing to do with IRCC decision on your study permit file.
In my place, I am gonna take another IETLS exam and try to score that least 7 in every section just to make my profile fit the school requirement and also to assure the vo that I am capable to survive in Canada and to success in my studies. You got band 6 in 2 sections, I guess reading and writing? How can a person with band 6 in writing accomplish the academic essays in an MBA program. That's not even enough for some Bachelors.
There must be things that you can improve in your SOP as well. It may be a common logic that MBA is an advancement in this case but you still have to tackle that basing on your own profile, experiences and future plans. As someone already said, MBA is a generic business program which you can take basically anywhere in the world. Is MBA from Canada better than some countries? Yes it is, but there are also better MBA elsewhere. Why Canada, why UNB, why MBA, why now. How does a MBA help you with your future professional plans? Don't use a sample SOP. That's the last thing you wanna do. Write it by your own and ask for someone to read it. Take it serious and if necessary, hire an Immigration Lawyer. Your chance now is modest due to the 2 previous refusals. Don't rush or you gonna close the door yourself.