how to get withholding tax back from US inland revenue nearly 2 years after the work was completed?

[Xxmmaass2015]

My husband (UK taxpayer) did some freelance work for an American university in February 2014, and the Inland Revenue Service deducted 30 % of his fee as withholding tax. HMRC in the UK assumed it would be refunded so he paid tax on the full sum in the UK, instead of on the 70 % he actually received.

IRS have been dragging their heels on refunding it, but when he spoke to them in Feb 2015, they said he would probably be given his money back by October 2015. October came but nothing happened, and every time he tried calling America he always ended up on hold for about an hour then would give up.

He just received a letter saying IRS needs another 6 months before they decide what action to take (i.e. in May 2016 he will get a decision on whether he even gets his refund, on money that was deducted from his earnings in February 2014).

He was counting on getting this sum of money in order to pay his upcoming tax bill by 31st January. What can we do?