Hello Pooja Khandelwal
If you have not manually declared / specified half fare, the ticketing system will not take it into account. How to specify the half fare option? See the screenshots in this reply:
https://community.sbb.ch/d/26418-how-can-i-save-the-info-of-swiss-half-fare-card
The half fare regular point-to-point ticket Zürich HB to Brienz via Brünig costs CHF 25.50, one way.
You may request a refund, yet you must first purchase the correct ticket, and this for the same route, same day, same passenger:
https://www.sbb.ch/en/help-and-contact/refunds-compensation/refunds-compensation/refund-form.html
Kind regards,
Roland