Payment Plan

Rent Arrears

Hi All,
After just over a year of being good with the payments, I currently have a tenant who has been behind on his rent for a few months now. Starting in late June he was short a small amount , the following month short by a larger amount and this month now the full rent hasn't been paid, and is now over 2 weeks late. The total amount owing is just under two months rent.
As per our last communication, I was expecting him to pay the full arrears today but instead I have a text message from him requesting to set up a payment plan, I've worked out it will take him 13 months to clear his arrears at this rate.
I have not been in this situation before and would like some advice. I do feel he has given me the run around, having promised twice before to pay off the full arrears and each time coming up with something else, so I definitely want to put something in writing if I decide to agree to this. Can anyone suggest a template for use in a situation like this.
Thanks in advance...