Easily. Just do a chargeback.
This applies to credit cards. If you're using debit cards, you're on your own.
First, make a modest effort to work directly with the vendor. The onus is on the vendor to be reasonably accessible: have an online site that actually provides a way to cancel that works; provide a customer service number that works, etc. Spend 10 minutes on this earnestly, and you have fulfilled this duty.
Then, contact your credit card company and report fraud and request a chargeback. Tell them about the reasonable efforts you made to contact the company, and that it's an auto renewal you don't want. You will get your chargeback. Others who are saying otherwise are just wrong.
The merchant has a tough time arguing
Mind you, there's some variation here, depending on what the goods are.
For any online service that is prepaid by the month or other period, like Major League Baseball live streaming (annually), Netflix (monthly) etc., it is impossible for the merchant to dispute the chargeback. The Bank's logic is very simple: the merchant is able to instantly disconnect your service. And the bank says "Look. If the customer doesn't want your service, stop selling it to them and walk away. If you want to snare the customer in lawyerly contract tricks, we won't help because that's bad business, we don't like to see that from businesses with a welcoming Mastercard sign on their door."
Virtual goods generally have so much merchant-side scamming that banks have little patience with it. If you buy Warcraft gold, and charge it back, Blizzard is expected to give you back your cash and use their god-power in-game to clawback the gold. A third party goldseller is just outta luck.
Now suppose it was a monthly stamp subscription. Every month they auto-sell you a roll of 100 stamps for $49. Stamps are fungible, easily converted to cash. And the good is physical and they have already shipped it. In this case, the merchant is likely to succeed in a chargeback. But not on the second chargeback a month later; the merchant should have known from the first chargeback that the customer doesn't want the good.
Casino chips are a more extreme example of "fungible to cash". A lesser example is event tickets; there's a tangible physical ticket and a vast underground economy for people to trade those tickets. Charging back tickets you have already printed out may meet resistance, especially if the event is over and the merchant can show the tickets were used. But again, banks expect merchants to "take a hint" and stop autocharging when the customer complains.
Chargeback only cancels the payment method
A chargeback only cancels the payment method, not the debt. So the merchant is at liberty to march down to the courthouse and use that reason (or any reason, as trumped up as they please) to sue you and try to collect that.
But the legal system isn't any more tolerant of bullpuckey than the banks. Much less in fact. The merchant is very likely to be handed their hat. And sanctions too, so at the least they should expect to pay defendant's legal fees, and at worst be barred from suing again without court oversight! The latter would apply if they tried to do this on a larger scale, e.g. Suing hundreds of cancellers. Righthaven, Prenda, etc.
Since a lawsuit is a lost cause, they'd be far more likely to just bill you a lot and threaten to take it to collection agencies. In fact, WIRED Magazine did that.
Of course, if the charges are part of a genuine, enforceable agreement or debt, this principle means you are still on the hook. I can't think of many examples of things typically paid for by credit card like this. But, say, if your landlord gives you the option to pay your rent by credit card, chargeback doesn't extinguish the need to pay rent, it just means you can't use a credit card anymore. Another example is a doctor's bill. Or your electric bill that you autpay via CC. Another, bless the few of you likely to commit to one of these, is an enforceable pledge to a charity.
But all these are plain debts that just happen to have an option by which they can be paid by credit card. Obviously you owe them.
Chargebacks equal consequences
What they won't be doing is re-charging your credit card for the amount you already disputed with additional fees. You'll simply dispute that, and the bank will read them the Riot Act, and this very negative attention in the fraud department will endanger their ability to remain a Visa/MC merchant.
Because yes. Merchants with excessive numbers of chargebacks face consequences, including withholding of substantial fractions of their money, higher transactional rates, and cancellation of their merchant services altogether.
A new merchant who is getting a lot of chargebacks could see ALL of his money frozen and held back to cover all the chargebacks the bank expects to have to give, which could be 100% if the product is fraudulent.