the short answer
Handle refunds and cancellations by deciding the rules before anyone pays and writing them into your coaching agreement: what is refundable, the notice period, how prepaid months are treated, and how to request it. When a request comes, reply fast and calmly, honour what you promised, and make leaving easy. A clear, fair policy prevents almost every dispute and chargeback.
If the agreement does not say any of that yet, the coaching contract generator writes the cancellation and missed-session clauses around the notice periods you pick, ready to print and sign.