This is a very common pb with every hotel booking engine (not only Accor) but I agree it should not happen with a pre-paid rate. I had this pb several times also. But as I have both visa and Amex, I always have one valid for the date of actual stay.
The pb with Accor pre-paid rates is that in many cases, they do not pre-charge and wait for your arrival at the hotel (and so they want a CC valid at the time of stay). In most cases you don't care but in your case...
The best way is may be to call the reservation center, as they may be able to proceed your card immediately (just my 2c )