24 hour fitness charging me for another subscription after cancellation houston Texas

So what you have just told us that in 10 months you failed to review your statements. If this is a debit card you also failed to reconcile your checking account in this amount of time. This also tells us that you have failed to provide proper account management for almost a year(at least). Where we can only hope that you don't have any other "invalid" charges showing up.

Now, I am not going to go into the whole "But they told me they would stop the withdraw". As yes they "should" have done that. But you "should" have also followed up.  "Trust but Verify".  It would have taken you 30 seconds to review your stamenent the first month to "verify" that they didn't charge you. But you failed to do that.  If you discovered this the first or even 2nd month, you would have a valid complaint   But at 10 months the responsibilty for this shifts to you.

Now you say...so they just have a right to take my money if it takes me 10 months to discover it.  The short answer is YES
and the Federal Goverment agrees.

Per the Fair Credit Billing Act, you do have liability protections against unauthorized charges. BUT it is up to the account holder(YOU) to report it within specified(and reasonable) time limits that would minimize the loss.

The FCBA gives you a maximum of 2 statements from the time the invalid charge appears to dispute it.  After that the card holder is 100% responsible for any "loss".  So if you have an issue with this perhaps you should take it up with the Federal Governemnt. Or better yet start to actually manage your accounts properly.