if you've got the calculation right, and unless you're unlucky enough to get audited, yes you'll get it. you won't get it quickly because the tax offices are suckered by tax credit paperwork.
if you can submit online though you'll jump the queue. either way, ring them up, be polite and stress that you need the money and chances are they'll get it to you as quick as possible. got my £5,000 rebate back in 4 days earlier this year, which was surprising!