What happens to your unused credit depends purely on the type of plan you are on. Currently, we sell two types of plans for our customers.
1) Monthly Plans
2) Pay as you go
If you are subscribed to a monthly plan, please see this article on Unused credit from a Monthly plan
If you have recently topped up your credit, please see this article on Unused Credit from a Top up
If you have any questions relating to this, get in touch with our billing department.