I assume you then suggested that Chase contact the merchant. How many more changes were submitted before it stopped? We went through something similar with a Citi VISA card, and it does appear that recurring charges from national merchants are treated differently than consumers might expect.
First of all, we did not even know there is an outfit called 24hr Fitness - I had to google it to find out who they are. The 1-800 number Chase gave it to me to call - assume it is from the identification of the charge - was answered by a call center located in Panama City, Panama, Central America. When I called about the first fraudulent charge, the "Senior Agent" could not find the card based on the number I gave it (per Chase CSR that the card was closed, so it would be safe to give it to the merchant - Duh!). When I called after the 2nd fraudulent charge happened some 3 weeks later, this time the "Senor Agent" could locate the card and said it was used by a woman in San Diego to pay for club due. The guy said the card was used at a club location, not a phone-in. He could see when the membership started (co-incided with the charge posted on Chase, i.e. confirmed by Chase?) but he could only see the actual charge of the 2nd one, the same date/amount as what went thru our card. I informed him this was being fraudulently used and please either deleted the card or at least put notation in the user's account that the fee was paid using fraudulently obtained CC info.
Chase wouldn't call the merchant - it is up to the consumer to stop such recurring frauds. The woman at Chase said the only way to stop the merchant is such fraudulent charges are being charged back and eventually the merchant would stop - who knows how long it would take? She said while we would receive another letter stemmed from the 2nd fraudulent charge, we could just add the 2nd fraudulent charge on the first letter. We finally received the first letter - and get this, it took 21 days from the letter issuance date to reach us, but the deadline to send it back was like less than a week from the date it arrived - rec'd it on 08/15 with deadline of 08/19. The fax number listed on the letter did not work for like 2 hours on a Tuesday morning...
I cancelled the replacement card the day after Chase credited back the 2nd fraudulent charge. I did not even bother to call, but requested cancellation WITHOUT GIVEN A REASON via the secured mail online. We will see if there would be any more fraudulent charge going thru.