To sue or not? Client stopped payment after cancellation period, but no services delivered.

I was hired in early December to cater a corporate holiday party for mid-January (200 guests). They requested to pay by check instead of credit card. Their accounting department took a while to process the check, so I didn't receive and deposit it until last Friday. My bank just informed me that the client stopped payment. I've emailed and called the client, and the only response I've received is an email that my services have been canceled. Because of the size of this event & menu I turned away other business while I was waiting for their check. Should I take them to small claims court? I've missed out on profits from other events that I could have booked for the same day. On their signed contract: "Cancellations after 12/13/15 forfeit any monies paid... Any monies paid is acceptance of the terms of this proposal.". The check they stopped payment on was for $6k which was for full payment except for tax and gratuity which they conveniently left off.