The vendor is under no obligation to provide a credit for a nonrefundable deposit, apply it towards another event, etc. when it (the vendor) was not the reason for the cancellation. If the wedding venue had cancelled, they would not entitled to keep the deposit, notwithstanding the language in the contract--they would have to refund it, or apply to another event at your direction. But since you were the one who cancelled, the venue is entitled to keep the deposit and not apply it to a future event, unfortunately.