Short Answer: File bankruptcy.
To “garnish” you, they need to have a judgment against you, which means that they already filed a lawsuit, a constable served you, they got a judgment, and they’ve contacted your employer to garnish your paychecks.
To take money out of your bank account, they don’t need any of this. All they need is a post-dated check or a signed ACH (electronic withdrawal authorization form) from you. They can hit your bank account over and over if you default on your payment plan with them. Bankruptcy does stop this, but if you cannot file bankruptcy yet, then you may want to contact your bank and tell them that you do NOT authorize any more electronic withdrawals from this creditor. This should keep them at bay until they do file a lawsuit.
And yes, even if they sue you and have a judgment, filing bankruptcy will stop the eventual wage garnishment and/or bank levy.