Do I have to give income and expenditure to Idem Servicing ?

I have a debt passed from Bank of Scotland to Idem Servicing. There isn't much left to pay on it (c £150). I've asked for a settlement figure but they've sent me a letter saying that they'll only accept the full amount.

I'll struggle to pay the full about in one month, but will be able to in three months or less. I know they'll probably want my income and expenditure but I'm uncomfortable discussing this with them. Do I have to give our these details?

And is there any point in trying to get a settlement figure less than the £150 or is that it? The debt was on a credit card and the amount left is pretty much added on fees from BoS.