Hi there,
They were exactly the same with me, and sent me on a bit of a run around. I eventually lost my temper and wrote to them stating the following -
"My IVA was completed on the 13 July, 2011, and if this is not marked as satisfied, it will not drop off my credit file in November, therefore, I must advise you that should this remain marked as incomplete on the 31st August, 2011 I will have no option than to complain to the Commissioner for Information and/or the Financial Ombudsman."
Needless to say, it was updated within the timescale I had set out. I gave them just over two weeks. It worked for me, so its worth a try, good luck