You made the contract, you should have put in a clause for termination of contract. I don't what sort of contract you are talking about. Anyway, the following section of the Employment Act could be of help to you.
"11. Provision as to termination of contracts.
(1) A contract of service for a specified period of time or for the performance of a specified piece of work shall, unless otherwise terminated in accordance with this Part, terminate when the period of time for which such contract was made has expired or when the piece of work specified in such contract has been completed."