If it was specified in the contract that delivery was to be by a certain date - and they then failed to meet that date - then you can demand the deposit back.

If, on the other hand, the delivery date was 'anticipated' to be by a certain point, then you may well find it's a lot more of a grey area.

I'd write to them, explaining that you view them to have breached the contract by being so long outside the original anticipated delivery date, and that you expect a full refund. Ask them that if they refuse to refund you, to supply you with their full company details by return, so that you can 'commence proceedings in the Small Claims Court'.

Whether you actually take it down that road is another matter entirely, of course ... but the threat often works.