My bank account was ach'd without my authorization...what can i do? ?

i bought an item at a furniture store and am making the payments through a 3rd party institute. we arranged it would be taken out every 29th of each month but they took it out on the 20th by mistake and now im overdrawn. any way i can get them to pay my overdrawn fees. any laws that can back me up. please and thank you..