I'm sorry but, this always happens before a sale. Somebody complaining about not getting the same for minutes, hours, etc.
Let's assume we'd make a rule such as "we'll do partial refunds if you buy 24 hours", you know what will happen then ? Somebody will say "hey I bought 24 hours + 40 minutes before the sale, can a get a discount ?", and what about those who bought 26 hours before, and why not just 27 ?
No, the one and only rule that is fair is, you either get the sale on time, or you don't, and I'm afraid you haven't.