I tend to remove the contents of company x and y envelope, put correspondence from x into prepaid envelope from company y and vice versa and put into post box. This then costs them the postage. If everyone did this junk mail would stop asap

I always send the forms back unsigned. A few days later, another pre paid envelope lands on the mat,"sorry,you forgot to sign this form." Send it back unsigned. A few days later........Have had Sun Life yo-yoing for months, lol. Gives me a hobby, keeps Postman Pat in a job, and costs the parasites money. Win-win.