Sorry to hear about your refusal.
order your GCMS notes, get to know the actual reason of VO.
Invitation from Canadian host isn't a enough proof that you will leave Canada after finish your trip . you need to demonstrate ties with your home country.
Try to travel more countries before apply to Canada ,thrice refusal it seems that you are desperate to move Canada.
you are still single at the stage of 30 years make no sense of strong Family ties + your permit is on temporary based.