PlusBus is a National Rail ticket, whose standard terms and conditions apply (including for ticket refunds). If you have bought a PlusBus ticket in advance from a station (or online) and do not want to use it, then you may claim a refund from the ticket office (or ticket retailer) that took original payment, but you must do this within 28 days of the travel date shown on the ticket. You must also return the ticket. Some ticket offices (and agents) may charge an administration fee of up to £10 to process refunds.
PlusBus tickets bought online may not be refundable from some online agents.
If you have a PlusBus season ticket and have used it for a while, but then want a refund of the outstanding period, you can claim a refund from the issuing ticket office. In this case normal National Rail season ticket refund terms and conditions apply.