Setting up payments with a payday loan company

I have contacted the payday loan companies I owe - the payments they want monthly are too high for me to do - they do not want to work with me on spreading out payments. I want to send a letter to them stating my own payment arrangements, my concern is that since it doesn't match what they said they "only could do" that the money I send will not be applied to my account. What can I do? I have been repeatedly contact my Payday Loan Debt Assistance out of Florida, but I'm shy of using such companies. Any advice?