Why am I being persued for x's legal aid expenses?

Hi Guys!
Im new to this forum, came highly recommended - by my Lawyer!!
However to cut a long story short, I am already divorced having been through the mills a couple of years ago. (Im happy to give my experience on that side of things if anyone needs...)
I have found myself now in a situation that has me baffled. During the divorce proceedings I always made it perfectly clear to my ex that I would not contest anything regarding the property, and matrimonial assests. I also made it clear that I was happy to remain "married" and let time resolve the issue of divorce. However she was insistant that a divorce was to be as quick as possible and as such started the proceedings through her Lawyer. She was granted full legal aid. After the divorce was complete, I recieved a letter from the legal aid board demanding the expenses. I contacted the legal aid board, explained my circumstances and even had a visit from one of their representatives. It was agreed that I was not in a position to pay the expenses. This was approx 6months ago and I hadnt heard anything since.
However, on Friday last week, I recieved a letter from her solicitor.
It is as follows:
Ms XP v Jambopiper
"We have been advised by the Scottish legal Aid Board of their difficulties in obtaining payment for the fees and outlays expended in the above action. They have intimated to us to apply to the court for a Decree for Expenses to assist them in recovery thereof.
We therefor hereby intimate you that a Diet of Taxation will take place within xxxxxxxxx, on Wed 4th june at 930am."
It goes on to ask wether I will be attending etc and if I could let them know....
Firstly, what is this, and secondly, how do I deal with it?
Just for the record - our divorce was an entirely mutual agreement, there was no third parties etc and basically she wanted to "move on". As said before, I did not contest (stupidly) anything, so she got the house, insurances etc etc. We have a daughter whom regularly stays over at mine etc, I pay an agreed amount faithfully every week via SO.
I am not in a position to pay the legal fees of some £3500 as I am self employed and barely make enough to survive as it is at present.
Any help would be greatly appreciated.