Spirit Airlines Spirit Air Refusal to honor voucher per advertisement , Internet

Had a travel voucher issued as apology for sudden cancellation of my reservation to Vegas 3 hours prior to departure.  (Was also offered a flight 3 days later to Vegas instead of a refund -- which was not helpful).  Was told to use the voucher within 60 days.  Made reservations to NYC for August 4.  Tried to use the voucher on their website, then when that failed, called in to customer service.  

The voucher redemption process is described on the Spirit website as follows:
"A Future Travel Credit can be used for all new bookings and can be used for the customer to whom it was issued."

However, I was told that the only flight to NYC that was available for voucher use was on August 14.  For the ENTIRE month of August.  They stated that, despite what their website states, they cannot use a travel voucher for any other date.  

To me, this smacks of false advertising as it directly contradicts their policy of course in a way to screw the customer.  I think that Spirit is such a terrible airline looking to cut as many corners as possible that I absolutely think that one of the planes will fall out of the sky soon.  And they will probably charge extra for a "quick landing."