Client unfaithful to payment due

The client signed a contract for us to market his business and when we completed the design and publication of a full banner advert, the client now ignores all our attempts to retrieve money for the work done. We have him (Mr Lovemore Wood)and an employee (Mrs Martha) on whatsap and they both create an impression that payment will be made but to date, we have met all the requirements and covered all costs incurred and now there is no care to make payment for work done