aca recoverycollecting for intsant cas how to deal with this,help plz

i get a letter from aca recovery saying they represent instant cash they say i owe them $650 .Besides this letter i also recieved a few phone calls from this moron who calls himself lopez.He called me on 3 seperate occasions.The last 2 calls he made he broke the fdcpa law by saying that a warrant for my arrest wil be issued if i dont call him by 5pm and it will go to legal matters the next day meanwhile this was weeks ago and nothing legal from them so far and i dont expect any.I sent them a debt validation letter to them certified mail and i did recieved it back with signature.Also in letter i told them i have never take a loan from instant cash(but after doing some research i have dicovered that the pay day loan i took from quickest cash is now called instant cash).I took outa $ 300 loan from them and i have paid them back 270 in interest so really i only owe them legaly is $30 i am in new york so i know pdls are prohibited here.After they got my dv letter they send 2 letters one day after the other saying same thing i owe 650 make payment to them.I call them up they tell me they never got my dv letter i have signature for proof.I then faxed them dv letters.Now i recieve from them the contract that i filled out on internet.What should i do next?how do i handle this?what should be my next step?