Hi Oldhack,
like lifenotsoeasy says, you definitely don't have to do that, you can ask for written proof of what you signed and agreed to, the owness is on them to demonstrate this and secondly if you did indeed sign something of which they did not clearly bring the changes to your attention then you can complain about this.
Grant Thornton (now APerture) are known for trying this sort of stunt and being hung out to dry by the regulators for all sorts of things,
so don't just accept it you wouldnt give a stranger knocking at your door 12 months extra payments so why give it to them if you're not legally or contractually bound to !
challenge it and do it all in writing so you can forward to the insolvency service and the regulators if needs be, it wouldn't be the first time they are wrong !
Here is a thread with their complaints procedure, escalate it all the way to risk and compliance (in writing)
GT COMPLAINTS
http://www.iva.co.uk/forum/topic.asp?TO ... hichpage=1
What the insolvency service says about someone changing your IVA terms and who to contact:
http://www.iva.co.uk/forum/topic.asp?TOPIC_ID=72957