Don't worry, you will get your money back if your payment went through and you didn't use that month, that only works if you canceled by may 30th. From June you owe them money, because remember just because you pay them equally montly payments dosen't mean thats what you're covered for each month. From June till about Oct is where the most of your insurance is distributed, from Nov to May if you cancel you owe them nothing they owe you if anything, the other months you owe them.
The payment that went through is gone and once you cancle the insurance company will send you cencelation package to TD insurance finance that close your accounts and will send you your check with the amount they owe you or you owe them. Its hard to tell in your situation who owes who because you're on the borderline of peak and non peak bike season cancelation period.
As for worrying about stealing your money, they can't, they will reimburse you if you are owed just takes 2 to 3 weeks, both the cancelation and agent you opened the accounts for are different departments. think of it this way you got full service and happy faces and everything doen on the spot when you opened your account because they wanted your money or business, but when you cancle they just need confirmation and basically say "F.U.K" you and send all the paper work to the back room "the financial departments to sort everything out and take their time closing your account and payments" btw Canada is not that currupt...yet! lol