Consider this, you add agents and delete them within your billing cycle. But you will be billed for the entire set of agents (including the deleted agents) for that cycle. The additional billing amount will be offered as credits which will be adjusted against the next billing cycle.
Credits have no currency or exchange value, they are non-transferable and non-refundable, and will expire following the termination of your paid services plan with Freshchat. Credits will be used against subsequently generated invoice(s).