CA refusing to send me anything in writing

I have another dilemma. I purchased a computer last year th Purchasing Power where the payments were taken directly out of my pay check through my employer. After a few decuctions, I moved out of state due to my pending divorce. I contacted the company immediately to set up alternate pymnt arrangements as per the contract agreement. They agreed to continue taking the same amounts out of my checking accounts until the computer was paid off. They took out 4 pymnts and then stopped. I contacted Purchasing Power and they told me that, for some reason, their computer was "kicking back" the decuctions from my checking account due to an address confliction with my debit card and my current address. I fixed that issue.
In the meantime, I started receiving letters from the company stating that I had not made a pymnt since I left my old employer and they were demanding pyment. The statement did not reflect the last four deductions from my checking account. I faxed them copies of my statement showing where they had indeed deducted the pymnts from my account and asked them to please send me a current corrected statement so that I could continue making my payments. I had to fax this info twice and was told both times that they would give the info to their accounting dept and get back with me. Noone would ever get back with me, and in the meantime, I'm still receiving these "Default Notices" every month which STILL do not reflect the the last four pyments from my checking account. I've left several messages for both the person who originally handled my account and the person who's name was on the letters.
I finally called back one last time a week ago after receiving the final Default Letter(this has been ongoing since July) and asked why no one had gotten back to me. I told them I would still like to continue the pymnts arrangements but needed something in writing showing they had posted the last four pyments. They only said that my account was extremely delinquent and they would no longer accept payment arrangements. They said they would accept the amount that I was claiming that I owed but still refused to send me anything in writing. I have kept every bit of paper work, fax confirmations and dates of conversations since July. What in the world do I do now? I do not have the money to pay the full amount ($750) and they're now threatening to report me to the CB's. I am hoping to be able to the balance in full when I receive my income tax return but that will not be for another month. All I want them to do right now is ackowledge that they've received those four pyments and send me an updated statemnt. If they don't, how do I know if I pay the balance,theywon't claim they never received it?