false pretenses

i had pictures taken by a professional photographer and excepted a package of photos, i picked the photos up from the photographer giving him partial payment with agreement to finish paying for them in future payments. due to unforseen curcumstances i have not been able to finish paying for the pictures the photographer has contacted me one time for the payment, now i have recieved a letter from the local police on the matter stating that i took these photo's under false pretenses and they are going to seek criminal charges unless i make payment in full, they have already sent a request to the prosecuter for review, what should i do