I owed for my 2017 taxes, and have paid the balance in full. How do I stop the automatic deductions from my bank account, now that my repayment is at a zero balance?

If you have paid off your balance in full, the payments should stop automatically.  If they have not, then you should call the agency responsible (the IRS or your state) and talk to them about stopping the payments.  Any payments in excess of what you owed are generally refunded, so be sure to ask if you can expect a refund when you call.