I wouldn't worry too much. Mine started processing on Aug 24th and I have my test next week. I can't exactly recall when I got the letter telling me the date but it was probably about 5 weeks ago.That is really terrible I feel bad for complaining I've been in process since Sept 12 and no test invite.
Have you tried phoning them?
I am curious how long it currently takes to go from test to oath. I'm seeing conflicting reports, although the cic website says within 3 months.