I keep meaning to stay there to sample what I think is the UKs cheapest HI, frequently to be found on IDEX for <£25 night! Never managed it though, dates just don't turn out right.

Over the past few months I have been offered varying points certs (CP 600, HI 500, HIX 300), or a drink and snack voucher every time I've checked in. There was notable exception, at the HI Leeds/Wakefield on a weekend stay. I remembered on the Saturday that I hadn't been offered the amenity, asked reception and received an apology for the lapse and both a cert plus a free drink and snack voucher.

I suspect in your case, like mine, it was forgotten. Ask at reception, even if the drinks voucher us no use to you now, the points cert should be!