are you on private or CSA collect hun?
if you are on private, you HAVE to collect it - you have no choice - if FAO find out you're not, they will cut your payment for not meeting the maintenance requirements
if you are CSA collect, they will keep a record of what you get. they will make sure you don't get overpaid - and if you do, they will reduce the amount of maintenance you get later to pay back the debt. they won't make YOU pay it back, they'll just give you less each month
if you are unsure, don't spend it - but if you've notified them he's unemployed, and they've still done this assessment, there is a reason behind it (and unless he can prove it should be otherwise, it should stand - if it does end up with the comment that you've been overpaid, you can appeal it based on you having told them the facts on x date)