how long?

I live in Ohio. I have a storefront payday loan with always payday. It was for $500 with a fee of $75. I was not able to pay it when i was due and i defaulted on my agreement. I then paid then $100, then another $100, leaving my balance at $399 left to owe because of the returned check charge in received from them for $24. At eh very end of sept. i received a letter from a local attorneys office about stating that i now owe $591, and for validation of the debt i needed to send a request within 30 days. At the beginning of october i mailed them my request for validation of the debt, and why i now owe $591, when i should only owe $399, and that i would be happy to set up a payment plan with them to take care of what i owe, upon validation of the debt. I mailed on oct 2, today id November 5, and i still have not received anything back from them. This office is a local office so i know if i mailed it on oct 2, they would have it in 1 to 2 business days. So should i worry? is there a limit of time in which they have to respond to me by in order for me to be held responsible?