Do you think my letter caused the company to take me to collections?

I got a settlement offer in the mail from Citibank to settle $4000 of debt for $2700. I sent a letter with a counter offer of $1500. Then company then sent me back a letter that stated" Thank you for you inquiry. Please contact our collections department to make payment arrangements." The letter only had a phone number to call. I then wrote the company back stating that I would not negotiate over the phone and that all negotiations had to be in writing along with an offer to send a money order of $1500 if the company would agree to remove all negative information and report the account as paid in full. Almost immediately after sending the letter, I get a phone call from a collection agency. I immediately hung up on the caller. I then got a letter stating that my account has been turned over to collections. Do you think the company sent it to collections because I insisted on only negotiating in writing?