I don't know how this case was and it agreement but I will also blame you in most of the cases like this. I have seen you giving a date to loan takers and when the particular time reached, you extent the date again probably there was a new agreement and if you are doing that way, many will default your loan. Always have a deadline with your clients.

Just a suggestion:
And remind the borrower regularly so that when date elapsed straight to accusation and you have to agree with him or her to pay you weekly every week until the payment complete. But when you extend, they use the money to do another thing and left yours because you normally extend.