if you are outside canada then you must inform them because then may be there is some different link to take the test. It is usually written in the document which you get to inform them at a particular email id.
Are you from Vancouver ? I dont think applicants have any rights to ask to change the processing center, although the processing center is allotted by their own process. Where are you stuck, no test invite ?
your application is stuck with some lazy officer. Just keep checking your tracker. there is nothing more you can do except order GCMS notes for your satisfaction to check what happened.