the child support thing may not have made a huge difference - there are amounts of payment you can receive that don't impact your payment much, so if it's dropped you from "just over" the income threshold for maintenance income, to "under" the threshold, the change to your payment would be minimal (very hard to explain without exact numbers)

there has to be more to it than meets the eye - getting rent assistance should increase your payment, not decrease it. i am wondering if it's to do with maintenance action - have you arranged your maintenance via the child support agency or privately? if it's been organised privately and not through the child support agency, it can result in your ftba dropping quite significantly