Legally speaking, digital downloads are slightly different from standard goods and services within British consumer rights. Generally speaking, you lose your rights to the 14-day cooling off period as soon as you download something (for obvious reasons). If you haven't provided consent by downloading, you may be able to get a refund on the basis of the standard legislation.
From a customer support standpoint, Rebellion may or may not add to said rights, but I've no idea if that's the case. Your best bet would probably be to call, explain what's happened, and ask if you can place an order over the phone there and then, along with immediately cancelling your access to the digital files. (Again, whether Rebellion has processes in place for this, I don't know.)