How do you convince them to be reasonable?

How do you convince them to be reasonable? I have had a few that were okay, and they made a reasonable payment plan. But most of them insist on payments that are larger than the original payments (duh, I got behind on those, I certainly can’t afford more). And most of them want automatic transfer payments (except the ones who want western union (duh, I’m late on payments, I can’t afford $15 every month to pay for western union).

And how do you get them to agree in writing? I had one last year that told me they would cut the total due to half ($3,000 down to $1,500) if I would make larger payments. It was tax refund time, I so I paid $650 in one shot, $350 a month later, and had agreed to two more payments of $250 to pay it completely off. After the first two payments, I got a phone call from them, and they wanted to arrange my next set of $350 payments. When I told them what I had left, they denied any such deal, and my balance due was $2,000. So, I made those larger payments (when I could have spread it out to my other bills), because of a deal that they promised and then denied. I had no proof of the deal. I really thought the deal was worth it to get rid of a complete bill quickly and lose $1500 of amount owed. But instead, I didn’t get rid of anything, and only delayed paying other bills down.

Also, another creditor insisted that a $500 payment would get me caught up, and then I would back to normal payments. After much harassment, I finally borrowed the money from my dad and paid the $500. Two weeks later, the guy called back and insisted on another $500. I think he figured I was holding out on the money, and since I had paid before, I could pay again. I told him I still hadn’t paid my dad back, and I couldn’t do it. He threatened wage garnishment, so I told him he lied to me in the past. I couldn’t give him something I didn’t have, and do what you gotta do. And I hung up on him. I went back to mailing in checks of $50 a month, and eventually, somebody else started the calls. We still haven’t worked out an agreeable plan. I just send my smal payments, and they just keep calling and telling me that is not enough. It’s a stalemate, but at least the lady is nice about it.

So, how do you get a payment plan that is reasonable? I have tried sending letters and asking for a payment plan in writing, but they ignored those.