Being harassed by MBD

MBD collectors are harassing me, it's two years paying my identity debt with them. They cannot provide me with a detailed statement to review the charges added to my debt. I believe I'm being over charged. Recently I have requested the contract in writing that stipulate the term of paying this term till to date I have not received that. I can't keep on paying for the sake of paying not knowing up until when. When they call I tell them I'm still waiting for a contract the consultant only want to know when am I going to make a payment about what I have requested from them they don't care about it.