Before you make payments to any service provider, you will be shown their cancellation policy. If they allow cancellation, it will be stated how much of a fine you will have to pay when you cancel and also until what date cancellation is possible. You will be responsible for paying whatever fine the service provider has assigned for cancellations if you wish to cancel.
If the service provider states that they do not allow cancellations, then, you will not be able to claim a refund on a service that you have booked and paid for. Please make sure your plans are certain before booking with any service provider in order to avoid complications.