Keep in mind that every time you lookup a carrier's name to verify its WSIB status, WSIB now has your "enquiring" name. Re the questionnaires which seem to be flooding from the WSIB offices these days, as long as you have a current CC, you are OK. You could print off and mail them back a copy of the letter and the current CC, and that should put an end to it. I had one re Aberstar, with an impeccable history of automatic renewals, yet the WSIB made an error and sent out the letters (I phoned WSIB to confirm). Were yours for Aberstar as well?
If I hadn't jumped on this right away, I would have thought Aberstar were deadbeats. If enough of those letters went out re Aberstar, they might have grounds for legal action against WSIB.