Got various £5 credits on Blinkbox almost a year ago (I think from HUKD tip off), and any unused credit is due to expire soon - mine are all 6th January - suspect others will be too.
Look on your Blinkbox a/c history at:https://www.blinkbox.com/account/history
"Use by ... 06/01/15"
If you have credits already expired, don't despair just yet...
bigredbucket reports below:
"Mine ran out on 19th December - but as for others, no reminders were sent out.
" I complained by email and they immediately re-instated the credit for 7 days to allow me time to spend it."
& Ch33ky reports below:
"Lost £15, but contacted them via live chat and they credited my account to use within 30 days. Worth a try"https://www.blinkbox.com/account/history