how to stop the ach debit?

Your bank will be able to take care of the matter. They can stop all ACH debits from the pdl place. The company will be blocked with their transaction code. This will not let them get money out of your account.

Your bank can stop ACH debits from pdls and any other type of business as long as you notify them in a timely manner before the ACH is scheduled to go through. There will most more than likely be a fee from the bank to stop these debits. Also, be careful though, b/c pdls are known to go by different names and if they submit an ACH with a different name, it will most more than likely go through your account.
Good Luck :D

Is it illegal to stop ach debits on your payday loan acct.

no it isn't.especially if the pdl is internet,illegal,and you've paid the principle in fees.even if the pdl is lega it isn't illegal.